Friday, March 15, 2013

Can we implement BGP without IGP Protocol ? If yes, then how can we do it ? If no, why ?


Hi,

Yes, for sure it is possible to configure BGP without any IGP. Check at these links where you can information and some examples:

Regarding your question, about IGP - If required or not depend in your design.
For example, if you have 2 facing routers to the Internet, both running BGP and with no direct connection between them:

R1   -   R2 -  R4  -   R3

Let suppose internet facing routers running BGP are R1 and R3. Then probably you need to synchronize BGP with a running IGP inside your core. That is to avoid the black hole created in R2 and R4.

but the major number one issue I would have is network convergence; which is very slow with BGP. timers are 60 and 180 ; of course u could change those.
other issues: BGP valid routes are based on path selection which is more complex than simple metric of OSPF or EIGRP. Configuration-wise, setting up BGP as IGP is complex and  challenging in contrast to IGP.
BGP is concern is stability and works perfect in routing Internet routes where changes do not happen to often; IGP are design for speed, fast recovery, re-convergence, multipath or load balancing traffic per default.

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BGP; Why we need to create static route to advertise a network?


Before BGP advertised its network, it checks the forwarding table for an exact match of network number and mask on router’s routing table.

R1 is expected to advertise network 128.20.0.0/16 and 10.10.10.0/24 to R2 using this configuration
router bgp 1
no auto-summary
network 128.20.0.0 mask 255.255.0.0
network 10.10.10.0 mask 255.255.255.0
However, when we check on R1, it is only 128.20.0.0 network that is being advertised.
R1#sh ip bgp    
BGP table version is 2, local router ID is 192.22.11.1
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
*> 128.20.0.0       0.0.0.0                  0         32768 i

R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C    128.20.0.0/16 is directly connected, Loopback0
C    192.168.20.0/24 is directly connected, Serial1/0.601
Also in R2, we only see network 128.20.0.0.
R2#sh ip bgp
BGP table version is 19, local router ID is 192.168.20.21
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
*> 128.20.0.0       192.168.20.20            0             0 20 i

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

B    128.20.0.0/16 [20/0] via 192.168.20.20, 00:06:58
C    192.168.20.0/24 is directly connected, Serial1/0.106
Aren’t 10.10.10.0/24 supposed to be advertised like 128.20.0.0/16?
Apparently NOT!
Why network 128.20.0.0/16 is being advertised? It is because network 128.20.0.0/16 has entry on router’s routing table and 10.10.10.0/24 is not.
R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C    128.20.0.0/16 is directly connected, Loopback0
C    192.168.20.0/24 is directly connected, Serial1/0.601
Again, on the first paragraph of this article, it’s stated:
Before BGP advertised its network, it checks the forwarding table for an exact match of network number and mask on router’s routing table.
Therefore, as no entry for 10.10.10.0/24 on the routing table, the network will not be advertised.
The solution is, if we want to include network 10.10.10.0/24 to be advertised, make sure that R1 has a component route for network 10.10.10.0/24 either by learning it through IGP or through static configuration. In the example shown, the static route is configured to null 0.
ip route 10.10.10.0 255.255.255.0 null 0
Now, let’s check the routing table on both R1 and R2.
R1#sh ip bgp
BGP table version is 3, local router ID is 192.22.11.1
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
*> 10.10.10.0/24    0.0.0.0                  0         32768 i
*> 128.20.0.0       0.0.0.0                  0         32768 i

R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C    128.20.0.0/16 is directly connected, Loopback0
     10.0.0.0/24 is subnetted, 1 subnets
S       10.10.10.0 is directly connected, Null0


R2#sh ip bgp
BGP table version is 24, local router ID is 192.168.20.21
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
*> 10.10.10.0/24    192.168.20.20            0             0 20 i
*> 128.20.0.0       192.168.20.20            0             0 20 i

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

B    128.20.0.0/16 [20/0] via 192.168.20.20, 00:01:12
     10.0.0.0/24 is subnetted, 1 subnets
B       10.10.10.0 [20/0] via 192.168.20.20, 00:01:12
NOTE. There is actually another way to do this. You can replace network 128.20.0.0 mask 255.255.0.0 with redistribute connected and replace network 10.10.10.0 mask 255.255.255.0with redistribute static. But still, you need to create a static routing for network 10.10.10.0/16 so that BGP able to see it from the routing table
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