Sunday, 14 April 2013

understanding ip networks: BGP PREFIX-LIST

understanding ip networks: BGP PREFIX-LIST: I have been using prefix-list right from where I started bgp. Now lets talk abt it Default prefix-list seq no is 5 and it also follow...
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understanding ip networks: AS-PATH ACCESS-LIST

understanding ip networks: AS-PATH ACCESS-LIST: Default config include bgp nei relationship and prefix advertisement R1..................... int s0/1 ip add 20.20.20.1 255.255....
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AS-PATH ACCESS-LIST



Default config include bgp nei relationship and prefix advertisement
R1.....................
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 10.10.10.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 10.10.10.2 remote-as 222
nei 20.20.20.2 remote-as 100
nei 20.20.20.2 next-hop-self
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
bgp router-id 150.150.150.1
no synchronization
network 150.150.151.0 mask 255.255.255.0

R2..................
int s0/0
ip add 30.30.30.2 255.255.255.0
no shut
int  s0/1
ip add 20.20.20.2 255.255.255.0
no shut
int s0/2
ip add 50.50.50.2 255.255.255.0
no shut
int lo 1
ip add 77.77.77.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
network 50.50.50.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
nei 50.50.50.1 remote-as 111
bgp router-id 77.77.77.1
no synchronization



R3..........................
int s0/0
ip add 40.40.40.1 255.255.255.0
no shut
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int lo 1
ip add 99.99.99.1 255.255.255.0
no shut
exit
router eigrp 1
network 30.30.30.0 0.0.0.255
network 40.40.40.0 0.0.0.255
no auto-summary
router bgp 100
nei 40.40.40.2 remote-as 222
nei 30.30.30.2 remote-as 100
nei 30.30.30.2 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
bgp router-id 99.99.99.1
no synchronization



ISP1..................................
int s0/0
ip add 50.50.50.1 255.255.255.0
no shut
int lo 1
ip add 200.200.200.1 255.255.255.0
no shut
exit
router bgp 111
nei 50.50.50.2 remote-as 100
bgp router-id 200.200.200.1
no synchronization



ISP2..................
int s0/1
ip add 40.40.40.2 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.2 255.255.255.0
no shut
int lo 1
ip add 100.100.100.1 255.255.255.0
no shut
int lo 2
ip add 100.100.101.1 255.255.255.0
no shut
int lo 3
ip add 100.100.102.1 255.255.255.0
no shut
int lo 4
ip add 100.100.103.1 255.255.255.0
no shut
exit
router bgp 222
nei 10.10.10.1 remote-as 100
nei 40.40.40.1 remote-as 100
bgp router-id 100.100.100.1
no synchronization
network 100.100.100.0 mask 255.255.255.0
network 100.100.101.0 mask 255.255.255.0
network 100.100.102.0 mask 255.255.255.0
network 100.100.103.0 mask 255.255.255.0


Task 1) ISP2 seems to be advertising prefixes that it does not originate making AS 222 a transit autonomous system. Configure ISP2 so that it only advertises its own prefixes.
Based on our topology, this cfg would not tell much because ISP is not connected to any other router asides from R1 and R3. But I would point out this config bcos it is important in production network
ISP2(conf)# ip as-path access-list 1 permit ^*
                     ip as-path access-list 1 deny .*                [not necessary since we have an implicit deny already]
                     router bgp 222
                    nei 10.10.10.1 filter-list 1 out
                    nei 40.40.40.1 filter-list 1 out
                    do clear ip bgp * in
                    do clear ip bgp * out

Toview changes made ,

                ISP2# sh ip bgp nei 10.10.10.1 advertised-route
               
(Recall I said earlier that this does not make a difference to what we av before)
   Network          Next Hop            Metric LocPrf Weight       Path
*> 100.100.100.0/24 0.0.0.0                                         0              32768 i
*> 100.100.101.0/24 0.0.0.0                                          0             32768 i
*> 100.100.102.0/24 0.0.0.0                                         0              32768 i
*> 100.100.103.0/24 0.0.0.0                                          0              32768 i



Task 2) On ISP1 filter out all prefixes originated by AS 222
Currently, on ISP1 bgp table
ISP1# sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 100.100.100.0/24 50.50.50.2                             0 100 222 i
*> 100.100.101.0/24 50.50.50.2                             0 100 222 i
*> 100.100.102.0/24 50.50.50.2                             0 100 222 i
*> 100.100.103.0/24 50.50.50.2                             0 100 222 i
*> 150.150.151.0/24 50.50.50.2                             0 100 i

ISP1(conf)# ip as-path access-list 1 deny _200$
                      ip as-path access-list 1 permit .*
                     router bgp 111
                      nei 50.50.50.2 filter-list 1 in
                      do clear ip bgp 50.50.50.2 in
                      do clear ip bgp 50.50.50.2 out

Now lets see the changes made
                ISP1# sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 150.150.151.0/24 50.50.50.2                             0 100 i

                ISP1# sh ip bgp filter-list 1            [to view bgp table with repect to the as-path filter-list]
   Network          Next Hop            Metric LocPrf Weight Path
*> 150.150.151.0/24 50.50.50.2                             0 100 i

ISP1# sh ip bgp nei 50.50.50.2 received-route
   Network          Next Hop            Metric LocPrf Weight Path
*  100.100.100.0/24 50.50.50.2                             0     100 222 i
*  100.100.101.0/24 50.50.50.2                             0     100 222 i
*  100.100.102.0/24 50.50.50.2                             0     100 222 i
*  100.100.103.0/24 50.50.50.2                             0     100 222 i
*> 150.150.151.0/24 50.50.50.2                             0   100 i

ISP1# sh ip bgp nei 50.50.50.2 route
   Network          Next Hop            Metric LocPrf Weight Path
*> 150.150.151.0/24 50.50.50.2                             0   100 i





Task 3) cfg AS 100 such that return path from AS 222 prefer R1
Currently on ISP2, bgp table is
   Network                           Next Hop            Metric                   LocPrf                   Weight                                 Path
*  99.99.99.0/24                 10.10.10.1                                                                           0                              100 i
*>                                           40.40.40.1               0                                                          0                              100 i
*> 100.100.100.0/24        0.0.0.0                  0                                                              32768                    i
*> 100.100.101.0/24        0.0.0.0                  0                                                              32768                    i
*> 100.100.102.0/24        0.0.0.0                  0                                                              32768                    i
*> 100.100.103.0/24        0.0.0.0                  0                                                               32768                   i
*  150.150.151.0/24         40.40.40.1                                                            0                              100 i
*>                                           10.10.10.1               0                                                          0                              100 i
*  200.200.200.0                40.40.40.1                                                                            0                              100 111 i
*>                                           10.10.10.1                                                                            0                              100 111 i

R3(conf)#            route-map n permit 10
                                set as-path prepend 100 100
                                exit
                                router bgp 100
                                neighbor 40.40.40.2 remote-as 222
                                neighbor 40.40.40.2 route-map n out
                                do clear ip bgp in 40.40.40.2
                                do clear ip bgp out 40.40.40.2
To view changes made,
ISP2#sh ip bgp
   Network                           Next Hop            Metric                   LocPrf                   Weight                                 Path
*  150.150.151.0/24         40.40.40.1                                                                            0                              100 100 100 i
*>                                           10.10.10.1               0                                                          0                              100 i
*  200.200.200.0                40.40.40.1                                                                            0              100 100 100 111 i
*>                                           10.10.10.1                                                                            0                              100 111 i
*> 99.99.99.0/24               10.10.10.1                                                                            0                              100 i
*                                             40.40.40.1               0                                                           0                             100 100 100 i

We can observer that AS 222 now prefers 10.10.10.1(R1) to reach AS 100










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BGP PREFIX-LIST


I have been using prefix-list right from where I started bgp. Now lets talk abt it
Default prefix-list seq no is 5 and it also follows the implicit deny all
permit 0.0.0.0/1 le 8
permit 128.0.0.0/2 le 16
permit 192.0.0.0/3 le 24

Default config include bgp  nei relationship and isp2 is advertising its network to all routers in the domain
R1.....................
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 10.10.10.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 10.10.10.2 remote-as 222
nei 20.20.20.2 remote-as 100
nei 20.20.20.2 next-hop-self
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
bgp router-id 150.150.150.1
no synchronization


R2..................
int s0/0
ip add 30.30.30.2 255.255.255.0
no shut
int  s0/1
ip add 20.20.20.2 255.255.255.0
no shut
int s0/2
ip add 50.50.50.2 255.255.255.0
no shut
int lo 1
ip add 77.77.77.1 255.255.255.0
no shut
exit
router eigrp 1
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
network 50.50.50.0 0.0.0.255
no auto-summary
exit
router bgp 100
nei 30.30.30.1 remote-as 100
nei 30.30.30.1 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
nei 50.50.50.1 remote-as 111
bgp router-id 77.77.77.1
no synchronization



R3..........................
int s0/0
ip add 40.40.40.1 255.255.255.0
no shut
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int lo 1
ip add 99.99.99.1 255.255.255.0
no shut
exit
router eigrp 1
network 30.30.30.0 0.0.0.255
network 40.40.40.0 0.0.0.255
no auto-summary
router bgp 100
nei 40.40.40.2 remote-as 222
nei 30.30.30.2 remote-as 100
nei 30.30.30.2 next-hop-self
nei 20.20.20.1 remote-as 100
nei 20.20.20.1 next-hop-self
bgp router-id 99.99.99.1
no synchronization



ISP1..................................
int s0/0
ip add 50.50.50.1 255.255.255.0
no shut
int lo 1
ip add 200.200.200.1 255.255.255.0
no shut
exit
router bgp 111
nei 50.50.50.2 remote-as 100
bgp router-id 200.200.200.1
no synchronization



ISP2..................
int s0/1
ip add 40.40.40.2 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.2 255.255.255.0
no shut
int lo 1
ip add 100.100.100.1 255.255.255.0
no shut
int lo 2
ip add 100.100.101.1 255.255.255.0
no shut
int lo 3
ip add 100.100.102.1 255.255.255.0
no shut
int lo 4
ip add 100.100.103.1 255.255.255.0
no shut
exit
router bgp 222
nei 10.10.10.1 remote-as 100
nei 40.40.40.1 remote-as 100
bgp router-id 100.100.100.1
no synchronization
network 100.100.100.0 mask 255.255.255.0
network 100.100.101.0 mask 255.255.255.0
network 100.100.102.0 mask 255.255.255.0
network 100.100.103.0 mask 255.255.255.0


Task 1) ISP1 should filter out prefixes 100.x.x.x.Use a sequence no of 10. Use prefix-list
Lets prove that ISP1 is getting the routes
ISP1# sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 100.100.100.0/24 50.50.50.2                             0 100 222 i
*> 100.100.101.0/24 50.50.50.2                             0 100 222 i
*> 100.100.102.0/24 50.50.50.2                             0 100 222 i
*> 100.100.103.0/24 50.50.50.2                             0 100 222 i

ISP(conf)# ip prefix-list A seq 10 deny 100.100.0.0/16 ge 24 le 24
                     ip prefix-list seq 20 permit 0.0.0.0/0 le 32
                     router bgp 111
                     nei  50.50.50.2 prefix-list A in
                     do clear ip bgp 50.50.50.2 in
                     do clear ip bgp 50.50.50.2 out

To view the changes made,
ISP1#sh ip bgp                                                                   [we see no routes]
ISP1#sh ip bgp nei  50.50.50.2 routes                       [w see no routes]
ISP1#sh ip bgp nei 50.50.50.2 received-route      [to display routes rcved from nei but not accepted]
   Network          Next Hop            Metric LocPrf Weight       Path
*  100.100.100.0/24 50.50.50.2                             0     100 222 i
*  100.100.101.0/24 50.50.50.2                             0     100 222 i
*  100.100.102.0/24 50.50.50.2                             0     100 222 i
*  100.100.103.0/24 50.50.50.2                             0     100 222 i




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Wednesday, 3 April 2013

BGP SOFT RESET CONFIGURATION



Default config: All bgp pairing have already been configured.
R1.....................
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
exit
router bgp 100
nei 10.10.10.2 remote-as 100
nei 10.10.10.2 next-hop-self
nei 20.20.20.2 remote-as 111
bgp router-id 150.150.150.1
no synchronization


R2..................
int s0/1
ip add 30.30.30.2 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.2 255.255.255.0
no shut
int lo 1
ip add 77.77.77.1 255.255.255.0
no shut
exit
router bgp 100
nei 10.10.10.1 remote-as 100
nei 10.10.10.1 next-hop-self
nei 30.30.30.1 remote-as 111
bgp router-id 77.77.77.1
no synchronization



ISP1..................................
int s0/0
ip add 20.20.20.2 255.255.255.0
no shut
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int lo 1
ip add 200.200.200.1 255.255.255.0
no shut
exit
router bgp 111
nei 20.20.20.1 remote-as 100
nei 30.30.30.2 remote-as 100
bgp router-id 200.200.200.1
no synchronization

Now lets face the problems

1) Cfg soft –reconfiguration on R2 for all its neighbors.  Hence clear the bgp on nei 10.10.10.2
R2(conf)#router bgp 100
nei 10.10.10.2 soft-reconfiguration inbound
nei 20.20.20.2 soft-reconfiguration inbound

[We don’t need to do in the outbound direction since it involves sending of routes it has received.]
To clear the nei 10.10.10.2,
R2# clear ip bgp 10.10.10.2 soft in
       clear ip bgp nei 10.10.10.2 soft out

2) cfg R2 to do a route-refresh. clear   nei isp1
Route-refresh do not actually require a config. We only need to check whether our router support this functionality.
R2#sh ip bgp nei 30.30.30.1
Route refresh: advertised and received (old & new)
We do the same on ISP1 to check whether it supports route-refresh..Then to clear the bgp nei,
R2#clear ip bgp 30.30.30.1 in
clear ip bgp 30.30.30.1 out
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OUTBOUND ROUTE FILTERING


This is a very cool feature cos it saves bandwidth. i.e. A will tell B that it does not need a set of routes, so B does not need to send it at all.
Default configs include ip address and bgp neighbor  relationship
r1
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int  s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 1.1.1.1 255.255.255.0
no shut
exit
ip route 22.22.22.0 255.255.255.0 s0/0
router eigrp 1
network 20.20.20.0 0.0.0.255
network 1.1.1.1 0.0.0.0
no auto-summary
exit
router bgp 100
nei 22.22.22.22 remote-as 222
nei 22.22.22.22 update-source lo 1
nei 22.22.22.22 ebgp-multihop 2
nei 2.2.2.2 remote-as 100
nei 2.2.2.2 update-source lo 1
nei 2.2.2.2 next-hop-self
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 next-hop-self
bgp router-id 1.1.1.1
no synchronization


r2
int s0/1
ip add 20.20.20.2 255.255.255.0
no shut
int  s0/0
ip add 30.30.30.2 255.255.255.0
no shut
int s0/2
ip add 50.50.50.2 255.255.255.0
no shut
int lo 1
ip add 2.2.2.2 255.255.255.0
no shut
exit
ip route 11.11.11.0 255.255.255.0 s0/2
router eigrp 1
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
network 2.2.2.2 0.0.0.0
no auto-summary
exit
router bgp 100
nei 11.11.11.11 remote-as 111
nei 11.11.11.11 update-source lo 1
nei 11.11.11.11 ebgp-multihop 2
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 next-hop-self
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 next-hop-self
bgp router-id 2.2.2.2
no synchronization


r3
int s0/1
ip add 30.30.30.1 255.255.255.0
no shut
int  s0/0
ip add 40.40.40.1 255.255.255.0
no shut
int lo 1
ip add 3.3.3.3 255.255.255.0
no shut
exit
ip route 22.22.22.0 255.255.255.0 s0/0
router eigrp 1
network 30.30.30.0 0.0.0.255
network 3.3.3.3 0.0.0.0
no auto-summary
exit
router bgp 100
nei 22.22.22.22 remote-as 222
nei 22.22.22.22 update-source lo 1
nei 22.22.22.22 ebgp-multihop 2
nei 2.2.2.2 remote-as 100
nei 2.2.2.2 update-source lo 1
nei 2.2.2.2 next-hop-self
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 next-hop-self
bgp router-id 3.3.3.3
no synchronization



ISP2
int s0/1
ip add 10.10.10.2 255.255.255.0
no shut
int  s0/0
ip add 40.40.40.2 255.255.255.0
no shut
int lo 1
ip add 22.22.22.22 255.255.255.0
no shut
int lo 2
ip add 23.23.23.23 255.255.255.0
no shut
exit
ip route 1.1.1.0 255.255.255.0 s0/0
ip route 3.3.3.0 255.255.255.0 s0/1
router bgp 222
nei 1.1.1.1 remote-as 100
nei 1.1.1.1 update-source lo 1
nei 1.1.1.1 ebgp-multihop 2
nei 3.3.3.3 remote-as 100
nei 3.3.3.3 update-source lo 1
nei 3.3.3.3 ebgp-multihop 2
bgp router-id 22.22.22.22
no synchronization


ISP1
int  s0/0
ip add 50.50.50.1 255.255.255.0
no shut
int lo 1
ip add 11.11.11.11 255.255.255.255
no shut
int lo 2
ip add 12.12.12.12 255.255.255.0
no shut
exit
ip route 2.2.2.0 255.255.255.0 s0/0
router bgp 111
nei 2.2.2.2 remote-as 100
nei 2.2.2.2  update-source lo 1
nei 2.2.2.2  ebgp-multihop 2
bgp router-id 11.11.11.11
no synchronization

1)  isp2 shld advertise network 23.23.23.0/24 out but isp1 shld not rcv it.Configure routers in such a way that changing the inbound filtering policy on ISP1 should force R2 to apply the right filtering preventing it from sending prefixes ISP1 does not wish to receive.
Lets confirm that ISP2 is advertising the route and also confirm ISP1 is receiving it
ISP2#sh ip bgp
*> 23.23.23.0/24    0.0.0.0                  0         32768 i

ISP1#sh ip bgp
   Network          Next Hop            Metric  LocPrf  Weight    Path
*> 23.23.23.0/24    2.2.2.2                                          0          100 222 i

Now lets configure routers ISP1 and R2
ISP1(conf)#ip prefix-list A seq 5 deny 23.23.23.0/24
                ip prefix-list A seq 10 permit 0.0.0.0/0 le 32
                router bgp 111
                nei 2.2.2.2 capability orf prefix-list send                 [ISP1 sends to R2 the routes it doesnot need]
                nei 2.2.2.2 prefix-list A in
                do clear ip bgp 2.2.2.2 in
                do clear ip bgp 2.2.2.2 out

Going to R2, we need to tell it to accept the orf prefix-list
R2(conf)#router bgp 100
                nei 11.11.11.11 capability orf prefix-list receive
                do clear ip bgp 11.11.11.11 in
                do clear ip bgp 11.11.11.11 out

Now lets prove that our config rocks
ISP1# sh ip bgp nei 2.2.2.2
  Outbound Route Filter (ORF) type (128) Prefix-list:
      Send-mode: advertised                          [advertised means ISP1 is cfged for send-mode]
      Receive-mode: received
  Outbound Route Filter (ORF): sent;
  Incoming update prefix filter list is A

R2# sh ip bgp nei 11.11.11.11
   Outbound Route Filter (ORF) type (128) Prefix-list:
      Send-mode: received
      Receive-mode: advertised
  Outbound Route Filter (ORF): received (2 entries)

R2#sh ip bgp nei 11.11.11.11 advertised-route
This displays empty route since ntwk 23.23.23.0 would not be sent to 11.11.11.11 bcos of the prefix-list

ISP1# sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 12.12.12.0/24    0.0.0.0                  0                  32768 i
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