03-31-2009 02:20 AM - edited 03-04-2019 04:10 AM
Hi,
I would like to confirm if I have two 3845 CE routers peering with say two 7206 routers.
7206-1 7206-2
| \/ |
ebgp /\ ebgp
| / \ |
3845-1 --ibgp-- 3845-2
In the above setup, the 3845-1 would be the primary router that sends and receive BGP routes from and to the site if it uses a higher loopback address. (bgp selection process)
This would mean that 3845-2 would be the secondary router in this scenario.
Pls advice,
Cheers,
- internetB -
Solved! Go to Solution.
03-31-2009 04:06 AM
Hello Shiva,
1) yes
2) no it is not enough to be sure incoming traffic will be sent to C3845-1
again the lowest BGP router-id is preferred not the highest: the BGP router-id is chosen as the highest loop ip address in the device. But even if C3845-1 has the lowest BGP router-id if in the SP network someone sends traffic to C7206-2 for any reason traffic will be sent to C3845-2.
Without using MED to indicate your preferred incoming point the SP can make different choices: this can be acceptable or not.
Hope to help
Giuseppe
03-31-2009 02:30 AM
Hello Shiva,
you may need to set MED for outbound routes and to set local-preference on received routes in order to achieve your objective.
set a lowest MED like 50 out 3845-1 and an higher metric 100 out 3845-2
route-map rise_metric1 permit 10
match ... ! acl here if needed
set metric 50
neigh 7206-1.ipaddr route-map rise_metric1 out
on c3845-2:
route-map rise_metric2 permit 10
match ... ! acl here if needed
set metric 100
neigh 7206-2.ipaddr route-map rise_metric2 out
set a local-preference higher then default 100 on c3845-1 for prefixes learned by c7206-1
neigh 7206-1.ipaddr local-preference 200
note: a lowest BGP router-id is preferred.
see
Prefer the route that comes from the BGP router with the lowest router ID
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml
Hope to help
Giuseppe
03-31-2009 02:34 AM
Hi Giuseppe,
I have seen this document before. My question was rather if I do not set any attribute, which would be the default router that the routes take for inbound/outbound traffic assuming that the bgp router-id is higher on 3845-1 ?
Thank you,
Cheers,
InternetB.
03-31-2009 02:37 AM
Hello Shiva,
I was modifying my first post.
I've provided there an example of what I would do to have C3845-1 to be preferred exit point and ingress point for traffic.
the MED is the right tool to influence how traffic is sent to you.
the local-preference helps to enforce C3845-1 as the preferred exit point
If using HSRP or GLBP having C3845-1 as the active router can be enough for the outbound direction.
Hope to help
Giuseppe
03-31-2009 02:55 AM
Hi Gieseppe,
1) So for outboung traffic, it depends which router is active on HSRP/GLBP and if we load balance the vlans on 3845-1 and -2 for active vlans, i guess we can load balance the outbound traffic right ?
2) Now for inbound traffic, would it all come to 3845-1 if no attributes are set assuming it has the higher router-id ?
Pls advice,
- InternetB -
03-31-2009 04:06 AM
Hello Shiva,
1) yes
2) no it is not enough to be sure incoming traffic will be sent to C3845-1
again the lowest BGP router-id is preferred not the highest: the BGP router-id is chosen as the highest loop ip address in the device. But even if C3845-1 has the lowest BGP router-id if in the SP network someone sends traffic to C7206-2 for any reason traffic will be sent to C3845-2.
Without using MED to indicate your preferred incoming point the SP can make different choices: this can be acceptable or not.
Hope to help
Giuseppe
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