What is split horizon?
Multicast address of rip v2?
What is the difference between rip and ripng?
What is the multicast address that rip v2 uses?
If a rip v2 router advertises its route, would it be received by all the devices on the network?
Can subnet mask information be stored in a rip v1 packet?
Rip v1 is a class full routing protocol. It does not understand classless concepts like subnets. So it is not possible.
Is a subnet mask field available in a rip v2 packet?
Rip v2 is classless routing protocol. A rip v2 packet has a field to include the subnet mask information.
What is eigrp?
Enhanced interior gateway routing protocol (eigrp) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by cisco systems as a proprietary protocol, available only on cisco routers.
What are the different tables in eigrp?
Neighbor table: the neighbor relationships are tracked in this table which are the basis for eigrp routing and convergence activity. The address and the interface of a neighbor is discovered and recorded in a new entry of the neighbor table, whenever a new neighbor is discovered. These tables are used for reliable and sequenced delivery of packets.
Topology table: routers use topology table which route traffic in a network. All routing tables inside the autonomous system are available in this table, where the router is positioned. Each router uses routing protocol and maintains a topology table for each configured network protocol. The routes leading to a destination are found in the topology table.
Route table: the routes of particular destinations are stored in the routing tables. The information contains the network topology that is immediately around it. The primary goal of routing protocols and routes is the construction of routing tables. Network id, cost of the packet path and next hop are the details are available in the routing table.
Why eigrp is called hybrid protocol?
Eigrp can be referred to as a hybrid protocol. It combines most of the characteristics of traditional distance vector protocols with some characteristics of link-state protocols. Specifically, eigrp is "enhanced" by using four routing technologies: neighbor discovery/recovery.
What are the different packets in eigrp?
- Hello packets: eigrp neighbor ship is discovered and maintained by hello packets. If the router fails to receive a hello packet within the hold timer, the corresponding router will be declared dead.
- Update packets: at the time of discovering new neighbor, update packets are sent, so that the topology table can be built by the neighbor router. Update packets are unicast and always transmitted reliably.
- query packets: when the destination goes into active state, the query packets are sent. Query packets are multicast and replies are always sent in reply to the queries for indicating the originator that it does not need to go into active state.
- reply packets: when the destination goes into active state, the reply packets are sent. Reply packets are unicast to the originator of the query and transmission of reply packets are reliable.
- ack packets: ack packets use to know the transmission status. If a hello packet sent without data is also recognized as acknowledgement. Unicast address with non-zero acknowledgement number is always sent by acks.
Conditions for eigrp neighbors ?
Both routers must be in the same primary subnet.
both routers must be configured to use the same k-values.
both routers must in the same as .
both routers must have the same authentication configuration (within reason) the interfaces facing each other must not be passive .
What is meant by active and passive states in eigrp?
A passive state indicates that a route is reachable, and that eigrp is fully Converged. A stable eigrp network will have all routes in a passive state. A route is placed in an active state when the successor and any feasible Successors fail, forcing the eigrp to send out query packets and reconverge. Multiple routes in an active state indicate an unstable eigrp Network. If a feasible successor exists, a route should never enter an active State.
Routes will become stuck-in-active (sia) when a router sends out a query Packet, but does not receive a reply packet within three minutes. In other Words, a route will become sia if eigrp fails to re-converge. The local Router will clear the neighbor adjacency with any router(s) that has failed to Reply, and will place all routes from that neighbor(s) in an active state.
Does eigrp require an ip default-network command to propagate a default route?
Although eigrp can propagate a default route using the default network method, it is not required. Eigrp redistributes default routes directly.
What are the different k-values used in eigrp?
1.Bandwidth (k1) 2. Load (k2) 3. Delay (k3) 4.Reliability (k4) 5.Mtu (k5).
What are the advantages of eigrp other routing protocol?
-Advanced distance vector
-Routes ip, ipx, decnet, appletalk
- Routing advertisements: partial when route changes occur
- Metrics: bandwidth, delay, reliability, load, mtu size
- Hop count: 255
- Variable length subnet masks
- Summarization on network class address or subnet boundary
- Load balancing across 6 equal or unequal cost paths (ios 11.0)
- Hello timer: 1 second on ethernet / 60 seconds on non-broadcast
- Holddown timer: 3 seconds on ethernet / 180 seconds on non-broadcast
- Metric calculation = destination path minimum bw * delay (msec) * 25
- Bidirectional forwarding detection (bfd) support
- Split horizon Lsa multicast address: 18.104.22.168
What is advertised distance?
Advertised distance or reported distance. The advertised distance (ad) is the distance from a given neighbor to the destination router. Feasible distance. The feasible distance (fd) is the distance from the current router to the destination .
What is successor?
A feasible successor is a path whose reported distance is less than the feasible distance, and it is considered a backup route. Eigrp will keep up to six feasiblesuccessors in the topology table. Only the one with the best metric (the successor) is placed in the routing table.
What is the multicast address used by eigrp to send hello packets?
What types of authentication is supported by eigrp?
Eigrp route authentication provides md5 authentication of routing updates from the eigrp routing protocol. The md5 keyed digest in each eigrp packet prevents the introduction of unauthorized or false routing messages from unapproved sources.
What is “stuck in active”?
When eigrp returns a stuck in active (sia) message, it means that it has not received a reply to a query. Eigrp sends a query when a route is lost and another feasible route does not exist in the topology table. The sia is caused by two sequential events: * the route reported by the sia has gone away.
What is the use of “variance” command in eigrp?
Eigrp provides a mechanism to load balance over unequal cost paths throungh variance command. Variance is a number (1 to 128), multiplied by the local best metric then includes the routes with the lesser or equal metric. The default variance value is 1, which means equal-cost load balancing.
What is feasible successor?
A feasible successor is a path whose reported distance is less than the feasibledistance, and it is considered a backup route. Eigrp will keep up to six feasible successors in the topology table. Only the one with the best metric (the successor) is placed in the routing table.
What is “graceful shutdown”?
This feature helps in faster convergence of networks. With graceful shutdown, a goodbye message is broadcast when an eigrp routing process is shutdown, to inform adjacent peers about the impending topology change.
How eigrp support unequal load balancing?
Eigrp supports up to six unequal-cost paths.
What happen when we enable passive interface in eigrp?
With eigrp running on a network, the passive-interface command stops both outgoing and incoming routing updates, since the effect of the command causes the router to stop sending and receiving hello packets over an interface.
Does eigrp support aggregation and variable length subnet masks?
Yes, eigrp supports aggregation and variable length subnet masks (vlsm). Unlike open shortest path first (ospf), eigrp allows summarization and aggregation at any point in the network. Eigrp supports aggregation to any bit. This allows properly designed eigrp networks to scale exceptionally well without the use of areas. Eigrp also supports automatic summarization of network addresses at major network borders.
Can i configure more than one eigrp autonomous system on the same router?
Yes, you can configure more than one eigrp autonomous system on the same router. This is typically done at a redistribution point where two eigrp autonomous systems are interconnected. Individual router interfaces should only be included within a single eigrp autonomous system. Cisco does not recommend running multiple eigrp autonomous systems on the same set of interfaces on the router. If multiple eigrp autonomous systems are used with multiple points of mutual redistribution, it can cause discrepancies in the eigrp topology table if correct filtering is not performed at the redistribution points. If possible, cisco recommends you configure only one eigrp autonomous system in any single autonomous system. You can also use another protocol, such as border gateway protocol (bgp), in order to connect the two eigrp autonomous systems.
What is the difference in metric calculation between eigrp and igrp?
1.Eigrp has totally replaced the obsolete igrp.
2. Eigrp is a classless routing protocol while igrp is a classful routing protocol.
3. Eigrp uses the dual while igrp does not.
4. Eigrp consumes much less bandwidth compared to igrp .
5. Eigrp expresses the metric as a 32 bit value while igrp uses a 24 bit value.
What is the eigrp stub routing feature?
The enhanced interior gateway routing protocol (eigrp) stub routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration. Stub routing is commonly used in a hub and spoke network topology.
How can i send a default route to the stub router from the hub?
Do this under the outbound interface on the hub router with the ip summary-address eigrp x 0.0.0.0 0.0.0.0command. This command suppresses all the more specific routes and only sends the summary route. In the case of the 0.0.0.0 0.0.0.0, it means it suppresses everything, and the only route that is in the outbound update is 0.0.0.0/0. One drawback to this method is that eigrp installs a 0.0.0.0/0 route to null0 is the local routing table with an admin distance of 5.
What are the primary functions of the pdm?
Eigrp supports 3 protocol suites: ip, ipv6, and ipx. Each of them has its own pdm. These are the primary functions of pdm:
- Maintaining the neighbor and topology tables of eigrp routers that belong to that protocol suite
- Building and translating protocol specific packets for dual .
- Interfacing dual to the protocol specific routing table.
- Computing the metric and passing this information to dual; dual handles only the picking of the feasible successors (fss) .
- Implement filtering and access lists.
- Perform redistribution functions to/from other routing protocols.
What are the various load-balancing options available in eigrp?
The offset-list can be used to modify the metrics of routes that eigrp learns through a particular interface, or pbr can be used.
Why are loopbacks advertised as /32 host routes in ospf?
Loopbacks are considered host routes in ospf, and they are advertised as /32.
Which command in ospf shows the network lsa information?
Show ip ospf 10 database network .
What command would you use to create a totally stubby area?
Router ospf 10 Area 10.
stub no –summary
What are area types? Why there are different area concepts?
-Standard areas can contain lsas of type 1, 2, 3, 4, and 5, and may contain an asbr. The backbone is considered a standard area.
-Stub areas can contain type 1, 2, and 3 lsas. A default route is substituted for external routes.
-Totally stubby areas can only contain type 1 and 2 lsas, and a single type 3 lsa. The type 3 lsa describes a default route, substituted for all external and inter-area routes.
- Not-so-stubby areas implement stub or totally stubby functionality yet contain an asbr. Type 7 lsas generated by the asbr are converted to type 5 by abrs to be flooded to the rest of the ospf domain.
What is the main importance of stub network? Why it is been developed in ospf?
A stub network is a somewhat casual term describing a computer network, or part of an internetwork, with no knowledge of other networks, that will typically send much or all of its non-local traffic out via a single path, with the network aware only of a default route to non-local destinations.
What will happen if we redistribute between different processes?
There can be several reasons for redistribution between multiple processes. These are a few examples:
- Filter an ospf route from part of the domain .
-Separate different ospf domains .
-Migrate between separate domains
What are lsa types?
Lsa type 1 (router lsa): Router link state advertisments type 1 are generated by every router for each link that belongs to an area. They are flooded only inside of area to which they belong. Link id of this lsa is the router id of the router that generated it.
Lsa type 2 (network lsa) :Generated by designated router (dr) for multiaccess networks and describe the routers that are connected to that segment. They are sent inside the area to which the network segment belong. The link id is the interface ip address of the designated router which describe that particular segment.
Lsa type 3 (summary lsa) :Type 3 lsas are generated by area border routers (abrs). In type 3 lsas are advertised networks from an area to the rest of the areas in as. Advertised networks in type 4 lsa can be summarized or not. The linkstate id used by this lsa is the network number advertised.
Lsa type 4 (summary lsa):- Generated by abrs, this type os lsa contain routes to asbrs. Link id used is router id of the asbr described. Are not flooded in stub areas.
Lsa type 5 (external lsa) :-Autonomous system external lsas are generated by asbrs and contain routes to networks that are external to current as. Link-state id is network number advertised in lsa. Type 5 lsas are not flooded inside any stub areas.
Lsa type 6 (multicast lsa) :This type of lsa is used for multicast applications.
Lsa type 7 (nssa external lsa):Type 7 lsa allow injection of external routes throug not-so-stubby-areas (nssa). Generally external routes are advertised by type 5 lsa but they are not allowed inside any stub area. That’s why type 7 lsa is used, to trick ospf. Type 7 lsa is generated by nssa asbr and is translated into type 5 lsa as it leaves the area by nssa abr, which is then propagated throughout the network as type 5 lsa.
Lsa type 8 (external attributes lsa for border gateway protocol (bgp): Used to work with bgp.
Lsa type 9,10,11 (opaque lsas) :- For future use.
What is ospf’s metric? How is it identified in routing table?
Does it support redistribution? Ospf uses a reference bandwidth of 100 mbps for cost calculation. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. For example, in the case of ethernet, it is 100 mbps / 10 mbps = 10. Note: if ip ospf cost cost is used on the interface, it overrides this formulated cost.
What are the states used in ospf when forming neighbor ship?
2-way. The 2-way state indicates that the local router has received a hello packet with its own router id in the neighbor field. Thus, bidirectional communication has been established and the peers are now ospf neighbors.
Types of ospf packets ?
1. The hello packet: the hello packets are sent over a period of time on all interfaces for the purpose of establishing and maintaining neighbor relationships. Hello packets are multicast on the networks having multicast capability, which enables discovery of neighboring routers dynamically. The inhabitance of differences among hello packets can form neighbor relationships by agreeing certain parameters.
2. The database description packet: at the time of adjacency is being initialized, these packets are exchanged. These packets describe topological database contents. The database may be described by using multiple packets. A pollresponse procedure is used for the description of multiple packets usage. Among the routers, one is designated to be master, and the other a slave. The database description packets are sent by the slave after sending the database description packets by the master.
3. The link state request packet: a router may find the parts of its topological database are out of date, after database description package exchange with a neighboring router. The link state request packet is utilized for requesting the pieces of the neighbor’s database which are more up to date. There may be a need to utilize multiple link state request packets.
4. The link state update packets: the flooding of link state advertisements is implemented by these packets. A collection of link state advertisements are carried by each link statement update packet, one hop further from its origin. A packed may be included by several link state advertisements.
5. The link state acknowledge packets: the reliability of flooding link state advertisement is made by explicitly acknowledging flooded advertisements. The accomplishment of this acknowledgement is done through the sending and receiving of link sate acknowledgement packets. A single link state acknowledgement packet is used to acknowledge the multiple link state advertisements.
What is ospf router id and how is it elected?
Router id is 32 bit number similar to ip address. It is elected as highest ip address of loopback interfaces or highest ip of the active physical interfaces if loopback is not present. It can also be set manually but it will take effect when ospf process is reset completely or device is reloaded. There should be only one router-id per device running ospf to avoid database issues.
What is the dr/bdr in ospf? How these are elected and in what scenario?
Dr/bdr election happens in shared multi access network to avoid full mesh scenario. In shared environment, every ospf router will try to form neighbor ship with other router, so dr/bdr comes in to action and act as single point of contact. Neighborship will only form with dr and backup dr. Dr router will be the highest priority router and bdr will be second highest priority. If there is a tie, then highest router-id will be used to make the decision. Router id is elected as the highest numerical loopback ip or the highest physical active ip address or the interface ip which comes up first.
What is the multicast ips used by ospf? What multicast ip does dr/bdr router and non-dr use?
Ospf routers use 22.214.171.124 multicast ip address. However, in dr/bdr it uses 126.96.36.199 and 188.8.131.52. Dr/bdr will use 184.108.40.206 while replying to ospf routers in broadcast multi access network.
How do i change the reference bandwidth in ospf?
You can change the reference bandwidth in cisco ios software release 11.2 and later using the ospf autocost reference-bandwidth command under router ospf. By default, reference bandwidth is 100 mbps. The ospf link-cost is a 16-bit number. Therefore, the maximum value supported is 65,535.
How to generate default route in ospf?
There are two ways to inject a default route into a normal area. If the asbr already has the default route in its routing table, you can advertise the existing 0.0.0.0/0 into the ospf domain with thedefaultinformation originate router configuration command.
What is ospf super backbone area?
The idea is that this super backbone can override the default behavior of ospf and provide connectivity between customers without the need for crazy virtual-links or tunneling (can’t use vls across area 0 anyway).
What is the concept of auto-cost in ospf?
The default reference bandwidth for OSPF is 10^8 bps or 100Mbit. Increasing the reference-bandwidth allows a more granular OSPF design. If changed it should be changed on all routers in the OSPF domain.The reason you would change the reference-bandwidth is that you may have link faster than 100M in your network. If you have Gigabit networks but are using the default reference-bandwidth, then Gigabit links are equal in cost to fast Ethernet.
device(config)# router ospf
device(config-ospf-router)# auto-cost reference-bandwidth 500
How does ospf calculate it’s metric or cost?
Ospf uses a reference bandwidth of 100 mbps for cost calculation. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. For example, in the case of ethernet, it is 100 mbps / 10 mbps = 10. Note: if ip ospf cost cost is used on the interface, it overrides this formulated cost.
What algorithm is used by ospf if equal cost routes exist?
If equal cost routes exist, ospf uses cef load balancing.
Are ospf routing protocol exchanges authenticated?
Yes, ospf can authenticate all packets exchanged between neighbors. Authentication may be through simple passwords or through md5 cryptographic checksums. To configure simple password authentication for an area, use the command ip ospf authentication-key to assign a password of up to eight octets to each interface attached to the area. Then, issue the area x authentication command to the ospf router configuration to enable authentication. (in the command, x is the area number.)
Can we have ospf run over a gre tunnel?
Yes, refer to configuring a gre tunnel over ipsec with ospf.
What is the maximum number of ospf processes (vrf aware) on 7600/6500 platforms?
Cisco ios has a limit of 32 routing processes. Two of these are saved for static and directly connected routes. The cisco 7600 router supports 28 ospf processes per vrf.
Which switching technology reduces the size of a broadcast domain?
By using vlan technology we can reduces the size of Broadcast domain.Vlan (virtual local area network) is a logical grouping or Segmenting the devices under a single broadcast domain.As a result provides security and flexibility.
Which protocols are used to configure trunking on a switch?
Vlan trunking protocol (vtp) is a cisco proprietary protocol that propagates the definition of virtual local area networks (vlan) on the whole local area network. To do this, vtp carries vlan information to all the switches in a vtp domain. Vtpadvertisements can be sent over 802.1q, and isl trunks.
What is svi ?
A switched virtual interface (svi) is a vlan of switch ports represented by one interface to a routing or bridging system. There is no physical interface for the vlan and the svi provides the layer 3 processing for packets from all switch ports associated with the vlan.
What is meant by “router on stick” ?
Router-on-a-stick is a term frequently used to describe a setup up that consists of a router and switch connected using one ethernet link configured as an 802.1q trunk link. In this setup, the switch is configured with multiple vlans and the routerperforms all routing between the different networks/vlan.
Which are the two trunking protocols ?
Difference between isl & 802.1q. A single communication link called trunk is usedbetween devices to carry traffic which may belong to multiple vlans.There are two main types of encapsulation protocols called isl (inter switch link) which is cisco proprietary protocol and 802.1q which is an ieee standard.
Which protocol encapsulate etherframes ?
Isl encapsulates ethernet frames while 802.1q tags ethernet frame.
Which is the vlan not tagged by 802.1q ?
How to delete vlan information from switch ?
Difference between access and trunk mode ?
Access mode is used to connect end devices(host) to switches while trunk mode is used to connect between switches.
Difference between dynamic auto and dynamic desirable ?
Dynamic desirable: attempts to negotiate a trunk with the other end. Dynamic auto: forms a trunk only if requested by the other end .
What is the use of nonegociate command in switch ?
Nonegociate command disables automatic formation of trunk links. It will be good to configure trunk manually and give non-negociate command for security reason.
Explain different switch port modes ?
Trunk: forms an unconditional trunk
Dynamic desirable: attempts to negotiate a trunk with the far end
Dynamic auto : forms a trunk only if requested by the far end
Access: will never form a trunk
What is dtp?
Dynamic trunking protocol is used to automatically establish trunks between capable ports (insecure method).
Which is the command used to see trunk interfaces ?
Show interface trunk
Show interface fa1/0/13 trunk
Show interface fa1/0/13 switchport Show interface status | include trunk
What is the maximum number of vlans permitted in 802.1q and isl?
Maximum vlan permitted in 802.1q is 4094 .
Maximum vlan permitted in isl is 1000.
What is the header size of 802.1q ?
What is the difference between an access port and a trunk port?
As for the difference between trunks and access ports, a trunk does add dot1q or isl tags directly to frames and can exist on all or multiple vlans. While an access port only passes traffic from a set vlan but does not modify the frame with a vlan tag.
What is frame tagging and different types of frame tagging?
Vlan frame tagging is a technology which is used to identify the vlan that the packet belongs to. The vlan frame tag is placed on the ethernet frame when the ethernet frame reaches a switch from an access port, which is a member of a vlan.
What is a native vlan and what type of traffic will go through native vlan?
The native vlan is the only vlan which is not tagged in a trunk, in other words,native vlan frames are transmitted unchanged. Per default the native vlan isvlan 1 but you can change that:
#show interface fa0/8 trunk. Port mode encapsulation status native vlan. Fa0/8 on 802.1q.
What is inter-vlan routing?
Virtual lans (vlans) divide one physical network into multiple broadcast domains. But, vlan-enabled switches cannot, by themselves, forward traffic across vlanboundaries. So you need to have routing between these vlans which is calledintervlan routing.
What is spanning tree aka stp ?
Spanning tree protocol (stp) is a layer 2 protocol that runs on bridges and switches. The specification for stp is ieee 802.1d. The main purpose of stp is to ensure that you do not create loops when you have redundant paths in your network. Loops are deadly to a network.
How does stp maintain a loop-free network?
Spanning tree works by first using an algorithm to find redundant links in the lan and selecting the best paths. Its initial goal is to put all links in either forwarding or blocking. In the end, the links without a redundant link and the best links with a redundant link would be in forwarding state. The redundant links that weren’t as good as the selected links would be in blocking state.
Spanning tree cannot use multiple links to the same destination. There is no load-sharing feature with spanning tree. Any redundant link that is not as preferred is blocked (essentially shut down) until the primary link goes down. Because the “best ports” are put into forwarding state and the other ports are put into blocking state, there are no loops in the network. When a new switch is introduced to the network, the algorithm and port states are recalculated to prevent a new loop.
What parameters can be tuned to influence the selection of a port as a root or designated port?
-If a switch has multiple paths to reach the root bridge (root switch), it must select one path and the associated port as the root port. Following are the different steps for selecting the root bridge (switch).
- Spanning tree root port selection process in a non-root switch involves the following steps.
- Select the port connected to the path with the lowest accumulated spanning tree path cost to theroot bridge (root switch) as the root port, when a non-root switch has multiple paths to reach the root switch.
- If multiple paths are available to reach the root bridge (root switch) with the same accumulatedspanning tree path cost in a non-root switch, select the port connected to the neighbor switch which has the lowest switch id value as the root port.
- If all the multiple paths go through the same neighboring switch to reach the root bridge (root switch), non-root switch will select the local port which receives the lowest port spanning tree port priority value from neighbor switch as the root port.
- If the received spanning tree port priority value values are the same between the connecting ports to reach the root bridge (root switch), non-root switch will select the port which receives the lowest physical port number from neighbor switch as the root port.
What is bdpu ?What is the basics function of bpdu?
The spanning tree protocol (stp) enabled switches in a redundant local area network (lan) need to exchange information between each other for spanning tree protocol (stp) to work properly. Bridge protocol data units (bpdus) are messages exchanged between the switches inside an interconnected redundant local area network (lan). Bridge protocol data units (bpdus) frames contain information regarding the switch id, originating switch port, mac address, switch port priority, switch port cost etc.
Bridge protocol data units (bpdus) frames are sent out as multicast messages regularly at multicast destination mac address 01:80:c2:00:00:00. When bridge protocol data units (bpdus) are received, the switch uses a mathematical formula called the spanning tree algorithm (sta) to know when there is a layer 2 switch loop in network and determines which of the redundant ports needs to be shut down.
Three types of bridge protocol data units (bpdus) are configuration bpdu (cbpdu), topology change notification (tcn) bpdu and topology change notification acknowledgment (tca). The basic purpose of the bridge protocol data units (bpdus) and the spanning tree algorithm (sta) is to avoid layer 2 switching loops and broadcast storms.
What is the stp listening state?
The ports on a switch with enabled spanning tree protocol (stp) are in one of the following five port states.
A switch does not enter any of these port states immediately except the blocking state. When the spanning tree protocol (stp) is enabled, every switch in the network starts in the blocking state and later changes to the listening and learning states.
Which command enables rstp on a switch?
Spanning-tree mode rapid-pvst
What is per-vlan spanning tree protocol (pvst).
A single spanning tree lacks flexibility in how the links are used in the network topology. Cisco implements a protocol known as per-vlan spanning tree plus (pvst+) that is compatible with 802.1q cst but allows a separate spanning tree to be constructed for each vlan.
What is the default bridge priority in a bridge id for all cisco switches?
Bridge id priority 32769 (priority 32768 sys-id-ext 1)
Which stp version run default on cisco switches ?
What is the purpose of spanning tree protocol in a switched lan?
The spanning tree protocol (stp) was designed to stop layer 2 loops. All ciscoswitches have the stp on by default. ... Convergence occurs when all ports on bridges and switches have transitioned to either the forwarding or blocking states. No data is forwarded until convergence is complete.
Difference between root port and designated port?
The differences between root port and designated port are listed below.
root port is a single selected port on a switch, other than root switch, with least path cost to reach the root bridge. The designated port is the port that has the lowest spanning tree path cost on a particular local area network (lan) segment.The root port is the port on the bridge (switch) with the least spanning tree path cost from the switch to theroot bridge.
A designated port is the port on a local area network (lan) segment with the least spanning tree path cost to the root bridge (root switch).there can be only one root port on a bridge (switch). There may be multiple designated ports on a bridge (switch).All the ports on a root bridge (root switch) are designated port and there is no root port on a root bridge (root switch).a root port can never be a designated port.if one end of a local area network (lan) segment is a designated port, other end is called as non designated port (marked as ndp), if it is not a root port. Non designated port will be always in blocking state, to avoid layer 2 switching loops.
What is the difference between path cost and root path cost?
Spanning tree uses costs associated to ingress ports to calculate the best path to the root bridge. The root path cost is the cumulative cost from the root to any given switch. Each port has a cost associated to it. On a cisco switch, the port cost can be altered using .
Sw1 (config-if)# spanning-tree [vlan vlan-id] cost cost
A third term exists which causes a little confusion: path cost. The path cost is the same thing as the port cost, just a different name for it.
What is the difference between stp, mstp, pvst and rstp?
Stp. Spanning tree protocol (ieee 802.1d). Forms a loop free graph (tree) in an arbitrary topology of switches. Gives you tools to set preferred location of a root and link costs for determining links to block.
Pvstp. Per-vlan spanning tree protocol . Cisco proprietary protocol that allows each vlan in a network to run an independent spanning tree with an independent root rather than forcing a single topology for all vlans.
Rstp. Rapid spanning tree protocol (ieee 802.1w). An evolution of the spanning tree protocol with faster convergence time, relying one some more advanced switch capabilities.
Mst. Multiple spanning tree protocol (ieee 802.1s). A standarized and evolved form of pvstp.
Etherchannel. A cisco technique that provides the ability to negotiate to bundle multiple physical links into a single, logical, higher speed link. (the standardized form is is ieee 802.3ad link aggregation) .
What is path cost?
Ports that are determined to have the lowest cost path to the root bridge are called designated ports. Switches or bridges running stp uses bpdu to exchange information.the bridge id is use to determine the root bridge and to determine the root port.
Define selection criteria of stp root bridge.
Spanning tree protocol (stp) is a layer 2 protocol that runs on bridges and switches. The specification for stp is ieee 802.1d. The main purpose of stp is to ensure that you do not create loops when you have redundant paths in your network. Loops are deadly to a network.
Why spanning tree bpdu filter is used?
The bpdu filter feature effectively disables stp on the selected ports by preventing them from sending or receiving any bpdus. Bpdu filtering supports the ability to prevent switches from sending bpdus on portfast-enabled interfaces. Ports configured for the portfast feature typically connect to host devices.
Can i use bpdu filter on trunk ports?
If a bpdu is received inbound when bpdu filter is applied globally then the portstops filtering and it will lose its portfast status. The bpdu guard default commandwill only apply to ports that are in a portfast operational state.
Which port state is introduced by rapid-pvst?
Which port state is introduced by rapid-pvst? Pvst+ is based on ieee802.1dspanning tree protocol (stp). But pvst+ has only 3 port states (discarding, learning and forwarding) while stp has 5 port states (blocking, listening, learning, forwarding and disabled).
What is spanning tree protocol (stp) portfast?
Spanning tree protocol (stp) convergence (layer 2 convergence) happens when bridges and switches have transitioned to either the forwarding or blocking state. ...portfast feature should be used only to connect a single workstation to a switch port to avoid layer 2 switching loop.
What does stp do when it detects a topology change in the network due to a bridge or link failure?
If spanning tree detects a change in the network due to a bridge or link failure, at least one bridge interface changes from the blocking state to the forwarding state, or vice versa.
How many root bridges can be available on a stp configured network ?
If the priority value of the two switches are same, which switch would be elected as the root bridge
Lowest mac address value
What is the basic purpose of the bpdus and stp?
To avoid the loop
What is configuration bpdu?
The default bpdu advertisement time of 2 seconds allows changes to be quickly shared with all the other switches in the network, reducing the amount of time any disruption would create. There are three kinds of bpdus: configuration bpdu, used by spanning tree protocol to provide information to all switches.
What is the destination mac address used by bridge protocol data units (bpdus)?
Bridge protocol data units (bpdus) are frames that contain information about the spanning tree protocol (stp). Switches send bpdus using a unique mac addressfrom its origin port and a multicast address as destination mac(01:80:c2:00:00:00, or 01:00:0c:cc:cc:cd for per vlan spanning tree).
What is tcn bpdu?
The root switch (bridge) bridge broadcasts the topology change information into the whole network. When a switch (bridge) discovers topology change, it generates atcn (topology change notification) bpdu (bridge protocol data unit) and sends the tcn bpdu on its root port.
What is tca bpdu?
The upstream switch (bridge) responds back the sender with tca (topology change acknowledgment) bpdu (bridge protocol data unit) and tca (topology change acknowledgment) bpdu (bridge protocol data unit) The process continues until the root switch (root bridge) receives the tcn bpdu.
What is bridge protocol data unit (bpdu) frame format?
Bridge protocol data units (bpdus) are frames that contain information about the spanning tree protocol (stp). Switches send bpdus using a unique mac address from its origin port and a multicast address as destination mac (01:80:c2:00:00:00, or 01:00:0c:cc:cc:cd for per vlan spanning tree).
What is root port?
The root port is the port on the bridge (switch) with the least spanning tree path cost from the switch to the root bridge. A designated port is the port on a local area network (lan) segment with the least spanning tree path cost to the rootbridge (root switch).
What is pvst or pvst+?
Overview of pvst and pvst+ per vlan spanning tree (pvst) is a cisco proprietary protocol that allows a cisco device to have multiple spanning trees. pvst+ is an extension of pvst that allows a cisco device to also interoperate with devices that are running a single spanning tree (ieee 802.1q).
What is extended system id?
The bridge priority value and the extended system id extension together make up a 16 bit (2-byte) value. The bridge priority making up the left most bits, is a value of 0 to 61440. The extended system id is a value of 1 to 4095 corresponding to the respective vlan participating in stp.
What are stp timers and explain different types of stp timers?
Important spanning tree protocol (stp) timers are hello timer, forward delay timer and max age timer and their default values are listed below.
Hello timer The hello timer is the time interval between each bridge protocol data unit (bpdu) that is sent on a port. Defaut spanning tree protocol (stp) hello timer is 2 seconds. You can adjust spanning tree protocol (stp) hello timer to any value between 1 and 10 sec. Click the following link to learn how to change the default spanning tree protocol (stp) hello timer.
Forward delay timer The forward delay timer is the time interval that is spent in the listening and learning state. Default spanning tree protocol (stp) forward delay timer is 15 seconds. You can adjust the spanning tree protocol (stp) forward delay timer to any value between 4 and 30 seconds.
Max age timer The max age timer controls the maximum length of time interval that a spanning tree protocol (stp) switch port saves its configuration bridge protocol data unit (bpdu) information. Default max age timer is 20 seconds. You can tune the spanning tree protocol (stp) max age timer to any value between 6 and 40 sec.