Saturday, 25 April 2020

BGP CHAPTER 4 - BGP CONFIGURATION USING LOOPBACK INTERFACES

!!Verifying Current Interface Configuration on R1 & R2

R1#sh int des

Interface                      Status         Protocol Description

Lo0                              up             up

Se0                               up             up       WAN CONNECTION 1

Se1                                up             up       WAN CONNECTION 2

R1#sh ip int brief

Interface                  IP-Address      OK? Method Status                Protocol

Loopback0             1.1.1.1                   YES manual    up                    up

Serial0                    12.1.1.1                  YES NVRAM  up                    up

Serial1                    21.1.1.1                   YES manual    up                    up


===========================================================

R2#sh int des

Interface                      Status         Protocol Description

Lo0                            up             up

Se0                            up             up       WAN CONNECTION 1

Se1                            up             up       WAN CONNECTION 2



R2#sh ip int brief

Interface                  IP-Address      OK? Method Status                Protocol

Loopback0              2.2.2.2         YES manual         up                    up

Serial0                    12.1.1.2          YES manual         up                    up

Serial1                    21.1.1.2           YES manual         up                    up

===========================================================

Currently no BGP configuration on both the Routers

R1#sh ip bgp sum



% BGP not active


R2#sh ip bgp



% BGP not active

===========================================================

Here there are two links between R1 and R2.



Establishing two BGP Neighborship using both paths is not a solution.



We need to establish only one BGP Neighborship between R1 and R2.

and this can  be achieved using loopback interfaces



So by using loopback interfaces for BGP neighborship.

=>we have both the path available.



=> BGP Neighborship wont go down even when the physical interfaces go down since loopback interfaces never goes down



BGP Neighborship “ LOOPBACK “ interfaces are always preferred .


======================================================================

By default BGP packets source is the outgoing interface but BGP gives us an option to change the source of the BGP packet sent.

Here we can use loopback interface as source of BGP packets sent between R1 and R2.

Hence we need to change source of BGP packet which can be achieved using "update source" command .

======================================================================

eBGP Neighborship should be directly connected i.e. same subnet .

By default TTL value in BGP packet is 1 when it enters from one AS to another AS.

But here we are using loopback interfaces which are in different subnet and they are not directly connected to each other .

Hence need to specify the same using eBGP multihop command

======================================================================

!! Configuration of the loopback interfaces

R1(config)#int loopback 1

Dec 13 01:54:28.959: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up

R1(config-if)#ip address 11.11.11.11 255.255.255.255

R1(config-if)#^Z

R2(config)#int loopback 1

Dec 13 01:55:33.523: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up

R2(config-if)#ip address 22.22.22.22 255.255.255.255

R2(config-if)#^Z

=======================================================================



R1(config)#router bgp 100

R1(config-router)#neighbor 22.22.22.22 remote-as 200

R1(config-router)#neighbor 22.22.22.22 update-source loopback 1

R1(config-router)#neighbor 22.22.22.22 ebgp-multihop 2


R2(config)#router bgp 200

R2(config-router)#neighbor 11.11.11.11 remote-as 100

R2(config-router)#neighbor 11.11.11.11 update-source loopback 1

R2(config-router)#neighbor 11.11.11.11 ebgp-multihop 2


R1#sh ip bgp sum

BGP router identifier 1.1.1.1, local AS number 100

BGP table version is 8, main routing table version 8

1 network entries using 117 bytes of memory

1 path entries using 52 bytes of memory

2/1 BGP path/bestpath attribute entries using 248 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 417 total bytes of memory

BGP activity 2/1 prefixes, 4/3 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

22.22.22.22     4   200       0       0        0    0    0 never    Active



R2#sh ip bgp sum

BGP router identifier 2.2.2.2, local AS number 200

BGP table version is 8, main routing table version 8

1 network entries using 117 bytes of memory

1 path entries using 52 bytes of memory

2/1 BGP path/bestpath attribute entries using 248 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 417 total bytes of memory

BGP activity 2/1 prefixes, 4/3 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

11.11.11.11     4   100       0       0        0    0    0 never    Active


R1#ping 22.22.22.22 source loopback 1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.22.22.22, timeout is 2 seconds:

Packet sent with a source address of 11.11.11.11

.....

Success rate is 0 percent (0/5)



BGP Neighborship is unsuccessful.

SINCE THERE IS NO L3 Reachability between the loopback interfaces .

No TCP session is established between them.


!!debug output on R2

Dec 13 02:28:40.475: BGP: 11.11.11.11 active open failed - no route to peer, open active delayed 34828ms (35000ms max, 28% jitter)


There should Reachability Between 11.11.11.11 & 22.22.22.22

Lets configure static routes for same .

R1(config)#ip route 22.22.22.22 255.255.255.255 s0

R1(config)#ip route 22.22.22.22 255.255.255.255 s1



R2(config)#ip route 11.11.11.11 255.255.255.255 S0

R2(config)#ip route 11.11.11.11 255.255.255.255 S1



!!debug output on R2

Dec 13 02:28:51.843: BGP: 11.11.11.11 passive open to 22.22.22.22

Dec 13 02:28:51.843: BGP: 11.11.11.11 went from Active to Idle

Dec 13 02:28:51.843: BGP: 11.11.11.11 went from Idle to Connect

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcv message type 1, length (excl. header) 26

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcv OPEN, version 4, holdtime 180 seconds

Dec 13 02:28:51.847: BGP: 11.11.11.11 went from Connect to OpenSent

Dec 13 02:28:51.847: BGP: 11.11.11.11 sending OPEN, version 4, my as: 200, holdtime 180 seconds

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcv OPEN w/ OPTION parameter len: 16

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcvd OPEN w/ optional parameter type 2 (Capability) len 6

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has CAPABILITY code: 1, length 4

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has MP_EXT CAP for afi/safi: 1/1

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcvd OPEN w/ optional parameter type 2 (Capability) len 2

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has CAPABILITY code: 128, length 0

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has ROUTE-REFRESH capability(old) for all address-families

Dec 13 02:28:51.847: BGP: 11.11.11.11 rcvd OPEN w/ optional parameter type 2 (Capability) len 2

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has CAPABILITY code: 2, length 0

Dec 13 02:28:51.847: BGP: 11.11.11.11 OPEN has ROUTE-REFRESH capability(new) for all address-families

BGP: 11.11.11.11 rcvd OPEN w/ remote AS 100

Dec 13 02:28:51.847: BGP: 11.11.11.11 went from OpenSent to OpenConfirm

Dec 13 02:28:51.847: BGP: 11.11.11.11 send message type 1, length (incl. header) 45

Dec 13 02:28:51.851: BGP: 11.11.11.11 went from OpenConfirm to Established

Dec 13 02:28:51.851: %BGP-5-ADJCHANGE: neighbor 11.11.11.11 Up


R1#sh ip bgp summary

BGP router identifier 1.1.1.1, local AS number 100

BGP table version is 9, main routing table version 9

2 network entries using 234 bytes of memory

2 path entries using 104 bytes of memory

3/2 BGP path/bestpath attribute entries using 372 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 734 total bytes of memory

BGP activity 3/1 prefixes, 5/3 paths, scan interval 60 secs



Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

22.22.22.22     4   200            13      13           9           0    0        00:08:21        1


R2#sh ip bgp summary


BGP router identifier 2.2.2.2, local AS number 200


BGP table version is 9, main routing table version 9


2 network entries using 234 bytes of memory


2 path entries using 104 bytes of memory


3/2 BGP path/bestpath attribute entries using 372 bytes of memory


1 BGP AS-PATH entries using 24 bytes of memory


0 BGP route-map cache entries using 0 bytes of memory


0 BGP filter-list cache entries using 0 bytes of memory


BGP using 734 total bytes of memory


BGP activity 3/1 prefixes, 5/3 paths, scan interval 60 secs




Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

11.11.11.11     4   100           14      14                     9    0    0           00:09:59        1



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



     1.0.0.0/32 is subnetted, 1 subnets

C       1.1.1.1 is directly connected, Loopback0

     2.0.0.0/32 is subnetted, 1 subnets

B       2.2.2.2 [20/0] via 22.22.22.22, 00:12:15

     21.0.0.0/24 is subnetted, 1 subnets

C       21.1.1.0 is directly connected, Serial1

     22.0.0.0/32 is subnetted, 1 subnets

S       22.22.22.22 is directly connected, Serial1

     11.0.0.0/32 is subnetted, 1 subnets

C       11.11.11.11 is directly connected, Loopback1



R1#sh ip bgp

BGP table version is 9, local router ID is 1.1.1.1

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

*> 1.1.1.1/32       0.0.0.0                  0           32768 i

*> 2.2.2.2/32       22.22.22.22              0             0    200       i

R2(config)#int s0

R2(config-if)#sh

R2(config-if)#^Z

Dec 13 02:44:47.415: %SYS-5-CONFIG_I: Configured from console by console

R2#sh ip bgp sum

BGP router identifier 2.2.2.2, local AS number 200

BGP table version is 9, main routing table version 9

2 network entries using 234 bytes of memory

2 path entries using 104 bytes of memory

3/2 BGP path/bestpath attribute entries using 372 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 734 total bytes of memory

BGP activity 3/1 prefixes, 5/3 paths, scan interval 60 secs



Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

11.11.11.11     4   100      20      20        9    0    0 00:15:59        1



POINTS TO REMEMBER
==========================
While using loopback address of eBGP configuration -


1)We need to change source of BGP packet which can be achieved using "update source" command .


2)Need to use eBGP multihop command.


3)THERE SHOULD BE Reachability BETWEEN loopback interfaces.


Thanks for the reading the blog !!!

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