Category Archives: Route

Here will categorize things about routers

BGP attributes: Weight

Facts about BGP weight attribute Cisco proprietary. Only available for Cisco routers, this attribute is not included in BGP update message. Because it is not included in update message, this attribute is only locally significant to one router. Because it … Continue reading

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Is full meshed iBGP necessary?

Revisit the configuration of the iBGP routers R2#sh run | s r b router bgp 2 bgp log-neighbor-changes neighbor 3.3.3.3 remote-as 2 neighbor 3.3.3.3 update-source Loopback2 neighbor 3.3.3.3 next-hop-self neighbor 4.4.4.4 remote-as 2 neighbor 4.4.4.4 update-source Loopback2 neighbor 4.4.4.4 next-hop-self … Continue reading

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IP routing with BGP

Problem 1: Did not receive prefix advertised by BGP peer. R2#sh ip bgp summary BGP router identifier 2.2.2.2, local AS number 2 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ … Continue reading

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Solving routing loop problem due to poorly configured redistribution

The diagram Routing loop when vIOS2 (R2) is trying to reach 1.1.1.1 in vIOS1 (R1) R2#traceroute 1.1.1.1 numeric Type escape sequence to abort. Tracing the route to 1.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 192.168.23.3 4 msec 4 … Continue reading

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Administrative distance

Administrative distance (AD) influences the decision on which routing protocol the router should trust: AD can be modified. AD is only locally significant to the router, other router’s AD of routing protocol might be modified. Router will use the routing … Continue reading

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Classless routing vs classful routing

Router routes traffic based on the longest prefix, and cannot find any match traffic will be dropped. Classless routing The routing that we normally understand is classless routing. Let’s explore the routing tables of R1 and R2. R1 pings to … Continue reading

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Unetlab: Backup static route is not used when peer router’s interface is down

Topology Background In GNS3 or in unetlab when the peer router’s (seemed) directly connected interface is down, your local router interface is still up. This is because the so-call directly connected is connected via a virtual bridge. In this lab … Continue reading

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