We have in fact requested that they allow us to add in /25 into their distribution list...
Now I have managed to add 2 static routes in my router
ip static route 22.214.171.124 mask 255.255.255.128 Gi 0/1
ip static route 126.96.36.199 mask 255.255.255.128 Gi 0/1
I managed to advertised out these 2 subnets to my neigbour.
Next, I tried to use route-map to influence my incoming traffic.
Say on the Internet, I want traffic going to 188.8.131.52 to use ISP A whilst traffic going to 184.108.40.206 to use ISP B.
A section of my route map is as below:
ip prefix-list prep_2000 seq 5 permit 220.127.116.11/25 ! ip prefix-list prep_3000 seq 5 permit 18.104.22.168/25 ! route-map PREPEND_3000 permit 10 match ip address prefix-list prep_3000 set as-path prepend 1000 1000 1000 ! route-map PREPEND_2000 permit 10 match ip address prefix-list prep_2000 set as-path prepend 1000 1000 1000
neighbor 22.214.171.124 route-map PREPEND_2000 out
neighbor 126.96.36.199 route-map PREPEND_3000 out
All works well. However, when I simulated that ISP A goes down, my client on the Internet cannot reach my internal clients on 188.8.131.52 /24.
When I look at the advertised routes from my router after applying the route maps, I noticed this:
#show ip bgp neighbors 184.108.40.206 advertised-routes BGP table version is 9, local router ID is 220.127.116.11 (My router interface) Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path *> 18.104.22.168/25 0.0.0.0 0 32768 i
Total number of prefixes 1
#show ip bgp neighbors 22.214.171.124 advertised-routes BGP table version is 9, local router ID is 126.96.36.199 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path *> 188.8.131.52/25 0.0.0.0 0 32768 i
Total number of prefixes 1
How can I advertise my 2 subnets to both my ISP and at the same time influence traffic in such a way that traffic going to 184.108.40.206 /25 uses ISP A (220.127.116.11) and traffic going to 18.104.22.168 /25 uses ISP A (22.214.171.124). When either ISP goes down, redundancy should be available to take the ISP whoever is available.
I am very new to BGP dual homing and prepending.. Appreciate the folks here can advice me...
What is happening is the route map's permit statement matches the prefix list and prepends the AS to that route. But if the route does not match the prefix list it is not advertised because you don't have a further permit statement.
So you need to add another permit statement to each route map. The second permit statement does not need any other configuration ie. you don't need to match anything with a prefix list and you don't need to set anything.
It just allows routes that are not matched in the first permit statement to be advertised.
Note after you modify the route maps you will need to reset the BGP session for it to take effect.
You may already aware but ISPs do not entertain advertising subnets with mask above /24. Unless you have another public subnet or your ISPs agree to accept /25, Iam afraid that you may not be able to achieve what you are looking for.
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