08-25-2012 02:35 AM - edited 03-04-2019 05:22 PM
Hello All,
I had a problem this morning and need your suggestion. We had a limited window so could not extend the troublesooting
router bgp 65457
no synchronization
bgp log-neighbor-changes
network 10.52.232.248 mask 255.255.255.248
aggregate-address 10.52.232.0 255.255.248.0 summary-only
redistribute static
neighbor 147.225.59.241 remote-as 65000
neighbor 147.225.59.241 route-map increase_weight in
default-metric 100000
no auto-summary
show run | s ip route
ip route 10.50.252.0 255.255.255.0 10.52.237.250 21
ip route 10.52.236.0 255.255.252.0 10.52.232.58
ip route 192.168.235.251 255.255.255.255 10.52.237.250
route-map increase_weight, permit, sequence 10
Match clauses:
ip address (access-lists): 10
Set clauses:
weight 40000
Policy routing matches: 0 packets, 0 bytes
route-map increase_weight, permit, sequence 20
Match clauses:
Set clauses:
Policy routing matches: 0 packets, 0 bytes
show access-lists 10
Standard IP access list 10
10 permit 10.50.252.0, wildcard bits 0.0.0.255 (5248 matches)
show ip bgp 10.50.252.0
BGP routing table entry for 10.50.252.0/24, version 781545
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Not advertised to any peer
65000 65000, (aggregated by 65457 10.50.252.254)
147.225.59.241 from 147.225.59.241 (159.24.197.199)
Origin IGP, localpref 100, weight 40000, valid, external, atomic-aggregate, best
show ip route 10.50.252.0
Routing entry for 10.50.252.0/24
Known via "bgp 65457", distance 20, metric 0
Tag 65000, type external
Advertised by bgp 65457 (self originated)
Last update from 147.225.59.241 01:51:08 ago
Routing Descriptor Blocks:
* 147.225.59.241, from 147.225.59.241, 01:51:08 ago
Route metric is 0, traffic share count is 1
AS Hops 2
Route tag 65000
10.50.252.0/24 is the prefix advertsied by remote site A
We want CR1 (in data center) to advertise 10.50.252.0/24 as soon as remote site MPLS goes down.
So we increased the weight by calling in bound route-map on CR1, so that CR1 learns this from its
ebgp peer(as long as the remote site MPLS is up). When remote site MPLS is down, we found that the route
is not advertised to any peer.
unfortunately, i lost the show ip bgp 10.50.252.0/24 on cr1 when remote site MPLS was down. there was
a route with weight 32768 but "not advertised to peer) not sure why
09-07-2012 06:32 AM
Thank you both
I would prefer doing it this way:
1. On remote site, I will prepend out the back up prefix with local as 5 times. I do not have any other bgp prefix with as path : 65000 65000 65000 65000 65000 in my current bgp table. Keeping in mind that 65457 will be rewritten as 65000 due to as override.
2. On HQ, I match this as-path using inbound route-map (via as-path acl) and set weight to 40,000 which is better than my locally sourced route.
In this way, I distinguish primary and backup route. Am I in the right track??
09-07-2012 06:47 AM
Hi,
no, you are assigning weight 40 000 to all prefixes with IP address=10.50.252.0/24 already.
So in the step 2. you need to match the prefix IP address=10.50.252.0/24 and AS_PATH=^65000 65000$ and deny such a prefix.
HTH,
Milan
09-07-2012 07:15 AM
route-map test, deny, sequence 10
Match clauses:
ip address (access-lists): 10 ------------------------- access-list 10 permit 10.50.252.0/24
Ip as-path ACL 10---------------------Ip as path acl 10 permit 65000 65000
route-map test, permit, sequence 20
Match clauses:
ip address (access-lists): 10 -------------------------access-list 10 permit 10.50.252.0/24
ip as path ACL 20--------------- ip as-path acl 20 permit 65000 65000 65000 65000 65000
Set weight: 40000
route-map test, permit, sequence 30
Match clauses:
Set clauses:
Policy routing matches: 0 packets, 0 bytes
09-07-2012 08:09 AM
Hi,
just be sure Ip as path acl 10 to permit ^65000 65000$ only.
Otherwise it could match also 65000 65000 65000 65000 65000 and the route-map would not work properly.
Or it might be worth to swap sequence 10 and 20 in your route-map?
BR,
Milan
09-07-2012 06:58 AM
Hi Giuseppe,
why do you think that "... the PE node behaviour is not correct even if configured with AS override it should not reflect back the route"?
Thanks,
Milan
09-04-2012 06:44 AM
Hi Vinayaka,
I notice you used the 'as soon" expresion in your explanation therefore I would recommend using the ip sla feature from Cisco to track the remote site reachability and insert a floating static route in case it times out.
ip sla monitor 1
type echo protocol ipIcmpEcho 1.1.1.1 source-ipaddr 2.2.2.2
timeout 3000
threshold 2000
frequency 5
!
ip sla schedule 1 life forever start-time now
!
track 1 rtr 1 reachability
For this you need to create an ip sla monitor,schedule, track it, as you can see above and change the static route to
ip route 10.50.252.0 255.255.255.0 10.52.237.250 21 track 1
You will not need a route-map to set any BGP attribute and the timers for ip sla will be at your disposal to change for your environment.
Take care,
PaulC
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