06-05-2008 01:52 AM - edited 03-05-2019 11:26 PM
Hi all, we have 2 routers using glbp, and bgp for the wan connection, my question is, they have 1 connection each to the lan, and one connection plugs directly into each other, what is this used for ?
06-05-2008 06:51 AM
That actually depends on the design, and boils down to the configuration.
Majorly, its used as a backup for FHRPs ( HSRP, VRRP, GLBP etc) in case we lose any of the uplinks.
Secondly, it prevents traffic blackhole in certain scenarios due to node/link failure.
AGain, it depends how its configured. The scenarios descried above works only if its in L2-mode.
Alternatively, it can be used as L3 link for route maintenance and proper route summarization towards core.
Most modern networks utilize a hybrid form of it, combining L2/L3 modes and getting best of both worlds.
HTH
Raj
06-05-2008 07:45 AM
Im still unsure what you mean here, can you explain, I thought that if using a redundancy protocol both connections have to use the lan port, would the middle cable be more for routing ?
06-05-2008 09:34 AM
Right, for FHRP hellos, it uses lan link by default, but for predictable designs, lets say only a link loss is there , but the active HSRP router is still active and I dont want HSRP to failover and make 2nd one active (there can be numerous scenarios), I'll use dist-link to pass hellos.
Please refer to some design docs or CCDP curriculum for further details.
From a L3 point of view, its critical for route summarization and avoiding of traffic blackhole due to link failure.
HTH
Raj
07-26-2008 12:50 AM
Hi there, so, how do you make the hsrp hello's go through the dist link? i thought they would only talk on the lan link? also what would the routing protocol do with this link?
thanks
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