basic routing question

[jeffkim.cisco]

Please see the attachment picture.

Traceroute to 8.8.8.8 from R1.

R1's default gateway is EDGE-Router2.

To get to 199.9.9.9, the next hop is ASA.

ASA default gateway is EDGE-Router1.

EDGE-Router is learning full internet routing table from the ISP.

Traceroute goes out to the ISP.......Why is that?

[Jon Marshall · Accepted solution]

R1's default gateway (presumably a default route) should be the next L3 hop which is presumably the ASA and not a router two L3 hops away.

That aside though the route used by R1 is only relevant to R1 ie. it is not carried with the packets so every L3 device does it's own L3 lookup based on the contents of it's own routing table. So if the edge router connected to the ISP has a more specific route for the destination IP via the ISP then it will use that route rather than it's default route.

Is this what you were asking ?

Jon

[jeffkim.cisco]

Thank you both of you.

Very helpful.

[Julio E. Moisa]

Hi

It was a pleasure  

:-)

[Julio E. Moisa · Accepted solution]

Hi

Prefixes learned by an eBGP peer will always preferred than iBGP prefixes because how you mentioned eBGP has a lowest AD than iBGP, unless you are using any BGP attribute like weight, local preference, MED, etc. to manipulate the traffic as you require. 

You could configure the following lines in order to prefer the prefix 8.8.8.8/32 through Edge router 2:

Edge Router 1:

ip prefix-list LP seq 5 permit 8.8.8.8/32

route-map EDGE-R2 permit 5
match ip address prefix LP
set local-preference 40000

route-map EDGE-R2 permit 100

router bgp <AS>
Nei 2.2.2.2 route-map EDGE-R2 in
Nei 2.2.2.2 next-hop-self

clear ip bgp * soft

*Note: remember to configure the command line: next-hope-self between the iBGP peers (Edge R1 --- iBGP --- Edge R2) in order to have a valid route.

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:-)