03-03-2005 01:43 AM - edited 03-02-2019 09:59 PM
Lets say I have 3 routers named A, B, and C where routers A and C have one serial and one Ethernet. Router B has one Ethernet and 2 serials. A is connected to B via serial and then B is connected by the other serial interface to C. Each router also has its own AS defined in BGP with its local Ethernet network being advertised.
If each router has its own distinct Ethernet subnet advertised via BGP, what's the proper way to advertise the subnets in BETWEEN the routers? For example, if I am on the Ethernet segment of router C and I want to ping/telnet to the serial of router A... normally this would not be possible since router A would only advertise its ethernet segment. Would A advertise this segment or would B do it since they are both locally attached?
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03-03-2005 05:23 AM
You should also be able to advertise the subnet if you'd like. If it is a /30 you would do the following:
router bgp
network x.x.x.x mask 255.255.255.252
Of course the opposite router sharing that link would receive the update but wouldn't install it in the RIB since it already has a connected route for this same subnet but the router not sharing that link would.
Hope this helps,
03-03-2005 02:29 AM
I think it is possible to advertise host routes for each serial ip. I don't think it is possible to advertise the whole subnet that exists on serial links between the routers.
To advertise a host route for a serial interface ip, try:
router bgp nnnnn
network x.x.x.x 255.255.255.255 <----"x.x.x.x is the serial interface ip, /32 host mask"
!
ip route x.x.x.x 255.255.255.255 serialx/y/z
I am not sure what the expected behaviour is if you try to advertise a whole in-between-subnet via one router.
If you find this helpful, then please share your findings!
Regards,
Mustafa
03-03-2005 05:23 AM
You should also be able to advertise the subnet if you'd like. If it is a /30 you would do the following:
router bgp
network x.x.x.x mask 255.255.255.252
Of course the opposite router sharing that link would receive the update but wouldn't install it in the RIB since it already has a connected route for this same subnet but the router not sharing that link would.
Hope this helps,
03-03-2005 02:59 PM
So all that needs to be done is to pick one of the routers that's connected and to the /30 subnet and have it advertise the subnet. It seems like it wouldn't matter which one is used. Is this correct?
Thanks!
Rob
03-03-2005 04:06 PM
You are correct indeed.
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