Dual ISP's for internet-changing weight

nygenxny123 · ‎07-01-2016

Yesterday we had an incident where one of our ISP's had a routing issue yet was still advertising

routes to us that were unreachable.

We have two ASR routers..one dedicated to ISP1 the other dedicated to ISP2

The ASR's are connected to each other via Gig ports..running BGP to each other also

ASR2 -going to ISP2 seems to be the preferred outbound internet route. MY question

is.

Would I simply add an increased weight on the the ASR2 /ISP2 so that outbound internet

routing than chooses ASR1 /ISP1?

ASR1(ISP1)
router bgp 51111
bgp log-neighbor-changes
network 50.xx.xx.0 mask 255.255.255.0
neighbor 10.43.x.2 remote-as 51111--------------ASR2
neighbor 10.43.x.2 update-source Loopback0
neighbor 10.43.x.2 next-hop-self
neighbor 205.x.x.7 remote-as 3111
neighbor 205.x.x.xx7 route-map Telco_in in
neighbor 205.x.x.xx7 route-map Telco_out out

ASR2 (ISP2)

router bgp 51111
bgp log-neighbor-changes
network 50.x.x.0 mask 255.255.255.0
neighbor 10.43.x.1 remote-as 51111--------------ASR1
neighbor 10.43.x.1 update-source Loopback0
neighbor 10.43.x.1 next-hop-self
neighbor 64.x.xx.2 remote-as 41113
neighbor 64.x.xx.2 route-map ISP_IN in
neighbor 64.x.xx.2 route-map ISP_OUT out

example--would like network 1.18.126.0 to have ASR1 as best route..ASR2 is advertised as the rout

ASR-1#sh ip route 1.18.126.0
Routing entry for 1.18.126.0/24
Known via "bgp 51111", distance 200, metric 0
Tag 4113, type internal
Last update from 10.3.x.2 1w3d ago
Routing Descriptor Blocks:
* 10.3.x.2, from 10.3.x.2, 1w3d ago-----------(ASR2 loopback address)
Route metric is 0, traffic share count is 1
AS Hops 3
Route tag 4113
MPLS label: none

ASR-1#sh ip bgp 1.18.126.0
BGP routing table entry for 1.18.126.0/24, version 510239969
Paths: (2 available, best #1, table default)
Not advertised to any peer
4113 4116 2119
10.3.x.2 (metric 2) from 10.3.x.2 (10.3.x.2) <--------ASR-2 Loopback
Origin incomplete, metric 0, localpref 100, valid, internal, best
219 6119 4116 21199
65.x.x.17 from 65.x.x.17 (205.x.x.150)
Origin IGP, metric 8000038, localpref 100, valid, external
Community: 136979

chrihussey · ‎07-01-2016

There are multiple was to accomplish this and setting the weight on ASR2 could work, but that would only be known to that router. It might be safer and cleaner to set the local preference for the routes from from ISP1 on ASR1 to a value higher than the default of 100. This attribute will propagate to ASR2 and both of your ASR routers will be on the same page and prefer the routes from ISP1.

Hope this helps.