Synchronization
Basic synchronization configuration
To enable traffic to be routed through multiple asynchronous systems (AS), IGP must propagate iBGP routes within its AS before they advertise them to peers outside its AS. All routers in an AS must learn of a route before BGP advertises the route outside of the AS. A BGP router must have synchronization disabled (the default setting) to validate these routes and install them into its routing table.
In this section, you configure BGP synchronization on the routers labeled BGP17,L BGP18, BPG19, BGP20, and BGP21 in the reference network diagram. The routers are advertising their routes on networks 10.0.40.0/24 and 10.0.50.0/24.
This section presents a sample configuration for BGP synchronization. The configuration example is based on the reference diagram in the following figure.
BGP synchronization must have AS200 configured as a transit between AS100 and AS300, and AS200 must have all routers meshed through iBGP.
BGP17 advertises a route to BGP18 through eBGP and the route is forwarded using iBGP to BGP20 through BGP19. For BGP20 to forward the route outside its AS to BGP 21, BGP19 must add the network in its routing table or the packet be dropped. BGP synchronization enables BGP19 to learn the network and to notify BGP20, before allowing BGP20 to forward the route to BGP21.
To create a basic BGP synchronization configuration, perform the steps in the following table:
|
Router |
Step |
Commands |
|---|---|---|
|
BGP17 |
Configure interfaces. |
|
|
BGP17 |
Establish BGP, by configuring BGP neighbors. |
|
|
BGP17 |
Advertise the route to establish the BGP route as the next hop and reachable. The eBGP route becomes an iBGP route. |
|
|
BGP18 |
Configure interfaces. |
|
|
BGP18 |
Establish BGP, by configuring BGP neighbors. |
|
|
BGP18 |
Advertise the route to establish the BGP route as the next hop and reachable. The eBGP route becomes an iBGP route. |
|
|
BGP19 |
Configure interfaces. |
|
|
BGP19 |
Advertise the route to establish the BGP route as the next hop and reachable. The eBGP route becomes an iBGP route. |
|
|
BGP20 |
Configure Interfaces |
|
|
BGP20 |
Establish BGP, by configuring BGP neighbors. |
|
|
BGP20 |
Configure synchronization and advertise the route to establish the BGP route as the next hop and reachable. The eBGP route becomes an iBGP route. |
|
|
BGP21 |
Configure Interfaces |
|
|
BGP21 |
Establish BGP, by configuring BGP neighbors. |
|
|
BGP21 |
Advertise the route to establish the BGP route as the next hop and reachable. The eBGP route becomes an iBGP route. |
|
Verifying the configuration
To display routes and their status for BGP 17, enter the command in the following example:
vyatta@BGP17# show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
> - selected route, * - FIB route, p - stale info
S *> 10.0.0.0/8 [1/0] via 10.1.34.1, dp0p160p1
C *> 10.1.34.0/24 is directly connected, dp0p160p1
O 20.1.1.0/24 [110/10] is directly connected, dp0p192p1, 15:39:00
C *> 20.1.1.0/24 is directly connected, dp0p192p1
O *> 30.1.1.0/24 [110/20] via 20.1.1.1, dp0p192p1, 00:26:54
O *> 40.1.1.0/24 [110/30] via 20.1.1.1, dp0p192p1, 00:26:54
O *> 50.1.1.0/24 [110/40] via 20.1.1.1, dp0p192p1, 00:26:54
C *> 100.1.1.0/24 is directly connected, dp0p224p1
C *> 127.0.0.0/8 is directly connected, lo
O *> 175.18.18.18/32 [110/20] via 20.1.1.1, dp0p192p1, 00:26:54
O *> 175.20.20.20/32 [110/40] via 20.1.1.1, dp0p192p1, 00:26:54
O *> 175.21.21.21/32 [110/50] via 20.1.1.1, dp0p192p1, 00:26:54
To verify the network, next hop routes, and their status in the BGP synchronization configuration, enter the command in the following example:
vyatta@BGP17# show ip bgp neigh 20.1.1.1 advertised-routes
BGP table version is 2, local router ID is 100.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.1.1.0/24 20.1.1.2 100 32768 i
Total number of prefixes 1
To display the routes and their status for BGP 18, enter the command in the following example:
vyatta@BGP18# show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
> - selected route, * - FIB route, p - stale info
S *> 10.0.0.0/8 [1/0] via 10.1.34.1, dp0p160p1
C *> 10.1.34.0/24 is directly connected, dp0p160p1
O 20.1.1.0/24 [110/10] is directly connected, dp0p192p1, 1d00h18m
C *> 20.1.1.0/24 is directly connected, dp0p192p1
O 30.1.1.0/24 [110/10] is directly connected, dp0p224p1, 21:20:09
C *> 30.1.1.0/24 is directly connected, dp0p224p1
O *> 40.1.1.0/24 [110/20] via 30.1.1.2, dp0p224p1, 16:28:46
O *> 50.1.1.0/24 [110/30] via 30.1.1.2, dp0p224p1, 00:50:46
B *> 100.1.1.0/24 [20/0] via 20.1.1.2, dp0p192p1, 00:28:08
C *> 127.0.0.0/8 is directly connected, lo
C *> 175.18.18.18/32 is directly connected, lo
O *> 175.20.20.20/32 [110/30] via 30.1.1.2, dp0p224p1, 00:40:19
O *> 175.21.21.21/32 [110/40] via 30.1.1.2, dp0p224p1, 00:44:16
To display advertised routes for BGP 18, enter the command in the following example:
vyatta@BGP18# show ip bgp neigh 175.20.20.20 advertised-routes
BGP table version is 3, local router ID is 175.18.18.18
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i100.1.1.0/24 20.1.1.2 100 0 100 i
Total number of prefixes 1
To display ospf updates for BGP 18, enter the command in the following example:
vyatta@BGP18# show ip ospf data
OSPF Router with ID (20.1.1.1) (Process ID 0)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
20.1.1.1 20.1.1.1 1338 0x80000180 0xc944 3
20.1.1.2 20.1.1.2 1740 0x80000172 0x4e29 1
30.1.1.2 30.1.1.2 1584 0x80000030 0x6ab7 2
40.1.1.1 40.1.1.1 656 0x8000002a 0x2bbe 3
50.1.1.2 50.1.1.2 906 0x80000007 0x86db 2
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
20.1.1.2 20.1.1.2 1736 0x80000007 0x2bc9
30.1.1.2 30.1.1.2 964 0x80000027 0x5462
40.1.1.1 40.1.1.1 1036 0x80000002 0x8a2b
50.1.1.2 50.1.1.2 1466 0x80000002 0x4e3d
AS External Link States
Link ID ADV Router Age Seq# CkSum Route Tag
100.1.1.0 20.1.1.1 1337 0x80000001 0x0537 E2 100.1.1.0/24 0
To display routes and their status for BGP 19, enter command in the following example:
vyatta@BGP19# run show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
> - selected route, * - FIB route, p - stale info
S *> 10.0.0.0/8 [1/0] via 10.1.34.1, dp0p160p1
C *> 10.1.34.0/24 is directly connected, dp0p160p1
O *> 20.1.1.0/24 [110/20] via 30.1.1.1, dp0p192p1, 15:18:49
O 30.1.1.0/24 [110/10] is directly connected, dp0p192p1, 20:58:07
C *> 30.1.1.0/24 is directly connected, dp0p192p1
O 40.1.1.0/24 [110/10] is directly connected, dp0p224p1, 16:08:04
C *> 40.1.1.0/24 is directly connected, dp0p224p1
O *> 50.1.1.0/24 [110/20] via 40.1.1.1, dp0p224p1, 00:30:04
O E2 *> 100.1.1.0/24 [110/1] via 30.1.1.1, dp0p192p1, 00:00:05
C *> 127.0.0.0/8 is directly connected, lo
O *> 175.18.18.18/32 [110/20] via 30.1.1.1, dp0p192p1, 00:25:26
O *> 175.20.20.20/32 [110/20] via 40.1.1.1, dp0p224p1, 00:19:36
O *> 175.21.21.21/32 [110/30] via 40.1.1.1, dp0p224p1, 00:23:34
To display advertised routes for BGP 20, enter the command in the following example:
vyatta@BGP20# show ip bgp neigh 50.1.1.2 advertised-routes
BGP table version is 6, local router ID is 175.20.20.20
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.1.1.0/24 50.1.1.1 100 0 100 i
Total number of prefixes 1
To display routes and their status for BGP 20, enter the command in the following example:
vyatta@BGP20# run show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
> - selected route, * - FIB route, p - stale info
S *> 10.0.0.0/8 [1/0] via 10.1.34.1, dp0p160p1
C *> 10.1.34.0/24 is directly connected, dp0p160p1
O *> 20.1.1.0/24 [110/30] via 40.1.1.2, dp0p192p1, 01:00:23
O *> 30.1.1.0/24 [110/20] via 40.1.1.2, dp0p192p1, 01:00:23
O 40.1.1.0/24 [110/10] is directly connected, dp0p192p1, 16:34:02
C *> 40.1.1.0/24 is directly connected, dp0p192p1
O 50.1.1.0/24 [110/10] is directly connected, dp0p224p1, 00:56:19
C *> 50.1.1.0/24 is directly connected, dp0p224p1
O E2 *> 100.1.1.0/24 [110/1] via 40.1.1.2, dp0p192p1, 00:26:20
B 100.1.1.0/24 [200/0] via 20.1.1.2 (recursive via 40.1.1.2 ), 00:26:44
C *> 127.0.0.0/8 is directly connected, lo
O *> 175.18.18.18/32 [110/30] via 40.1.1.2, dp0p192p1, 00:51:41
C *> 175.20.20.20/32 is directly connected, lo
O *> 175.21.21.21/32 [110/20] via 50.1.1.2, dp0p224p1, 00:49:48
To verify the network, next hop routes, and their status in the BGP synchronization configuration, enter the command in the following example:
vyatta@BGP20# show ip bgp
BGP table version is 6, local router ID is 175.20.20.20
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, l - labeled
S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i100.1.1.0/24 20.1.1.2 0 100 0 100 i
Total number of prefixes 1
To display received routes for BGP 21, enter the command in the following example:
vyatta@BGP21# show ip bgp neigh 50.1.1.1 received-routes
BGP table version is 8, local router ID is 175.21.21.21
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.1.1.0/24 50.1.1.1 0 200 100 i
Total number of prefixes 1
To display routes and their status for BGP 21, enter the command in the following example:
vyatta@BGP21# show ip routes
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
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, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
> - selected route, * - FIB route, p - stale info
S *> 10.0.0.0/8 [1/0] via 10.1.34.1, dp0p160p1
C *> 10.1.34.0/24 is directly connected, dp0p160p1
O *> 20.1.1.0/24 [110/40] via 50.1.1.1, dp0p192p1, 00:55:30
O *> 30.1.1.0/24 [110/30] via 50.1.1.1, dp0p192p1, 00:55:30
O *> 40.1.1.0/24 [110/20] via 50.1.1.1, dp0p192p1, 00:55:30
O 50.1.1.0/24 [110/10] is directly connected, dp0p192p1, 00:56:54
C *> 50.1.1.0/24 is directly connected, dp0p192p1
O E2 100.1.1.0/24 [110/1] via 50.1.1.1, dp0p192p1, 00:28:38
B *> 100.1.1.0/24 [20/0] via 50.1.1.1, dp0p192p1, 00:28:47
C *> 127.0.0.0/8 is directly connected, lo
O *> 175.18.18.18/32 [110/40] via 50.1.1.1, dp0p192p1, 00:54:00
O *> 175.20.20.20/32 [110/20] via 50.1.1.1, dp0p192p1, 00:48:10
C *> 175.21.21.21/32 is directly connected, lo
Graceful restart
To configure graceful restart if it has not been configured, enter the following command: