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diff --git a/docs/sources/ebgp-multihop.md b/docs/sources/ebgp-multihop.md new file mode 100644 index 00000000..8770daf7 --- /dev/null +++ b/docs/sources/ebgp-multihop.md @@ -0,0 +1,120 @@ +# eBGP Multihop + +This page explains how to configure eBGP multihop feature when external +BGP (eBGP) peers are not directly connected and multiple IP hops away. + +## Prerequisites + +Assume you finished [Getting Started](https://github.com/osrg/gobgp/blob/master/docs/sources/getting-started.md). + +## Contents + +- [Configuration](#section0) +- [Verification](#section1) + +## <a name="section0"> Configuration + +If eBGP neighbor "10.0.0.2" is 2 hops away, you need to configure +`[neighbors.ebgp-multihop.config]` with `multihop-ttl >= 3` in +`[[neighbors]]` section. + +```toml +[global.config] +as = 65001 +router-id = "10.0.0.1" + +[[neighbors]] + [neighbors.config] + peer-as = 65002 + neighbor-address = "10.0.0.2" + [neighbors.ebgp-multihop.config] + enabled = true + multihop-ttl = 3 +``` + +**NOTE:** eBGP Multihop feature is mututally exclusive with +[TTL Security](https://github.com/osrg/gobgp/blob/master/docs/sources/ttl-security.md). +These features cannot be configured for the same neighbor. + +## <a name="section1"> Verification + +Without eBGP multihop configuration, the default TTL for eBGP session is 1, +and GoBGP cannot reach the neighbor on 2 hops away. + +``` +$ gobgpd -f gobgpd.toml +{"level":"info","msg":"gobgpd started","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"Topic":"Config","level":"info","msg":"Finished reading the config file","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"level":"info","msg":"Peer 10.0.0.2 is added","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"Topic":"Peer","level":"info","msg":"Add a peer configuration for:10.0.0.2","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +...(No connection)... +``` + +``` +$ tcpdump -i ethXX tcp -v +tcpdump: listening on ethXX, link-type EN10MB (Ethernet), capture size 262144 bytes +hh:mm:ss IP (tos 0x0, ttl 1, id 19110, offset 0, flags [DF], proto TCP (6), length 60) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [S], cksum 0x8382 (incorrect -> 0x540e), seq 31213082, win 29200, options [mss 1460,sackOK,TS val 2231484 ecr 0,nop,wscale 9], length 0 +hh:mm:ss IP (tos 0x0, ttl 1, id 19111, offset 0, flags [DF], proto TCP (6), length 60) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [S], cksum 0x8382 (incorrect -> 0x5314), seq 31213082, win 29200, options [mss 1460,sackOK,TS val 2231734 ecr 0,nop,wscale 9], length 0 +hh:mm:ss IP (tos 0x0, ttl 1, id 19112, offset 0, flags [DF], proto TCP (6), length 60) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [S], cksum 0x8382 (incorrect -> 0x511f), seq 31213082, win 29200, options [mss 1460,sackOK,TS val 2232235 ecr 0,nop,wscale 9], length 0 +...(snip)... +``` + +With eBGP multihop configuration, GoBGP will set the given TTL for eBGP +session and successfully connect to the neighbor on 2 hops away. + +``` +$ gobgpd -f gobgpd.toml +{"level":"info","msg":"gobgpd started","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"Topic":"Config","level":"info","msg":"Finished reading the config file","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"level":"info","msg":"Peer 10.0.0.2 is added","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"Topic":"Peer","level":"info","msg":"Add a peer configuration for:10.0.0.2","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +{"Key":"10.0.0.2","State":"BGP_FSM_OPENCONFIRM","Topic":"Peer","level":"info","msg":"Peer Up","time":"YYYY-MM-DDTHH:mm:ss+09:00"} +...(snip)... +``` + +``` +$ tcpdump -i ethXX tcp -v +tcpdump: listening on ethXX, link-type EN10MB (Ethernet), capture size 262144 bytes +hh:mm:ss IP (tos 0x0, ttl 3, id 31155, offset 0, flags [DF], proto TCP (6), length 60) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [S], cksum 0x8382 (incorrect -> 0x42a8), seq 3226540591, win 29200, options [mss 1460,sackOK,TS val 3302300 ecr 0,nop,wscale 9], length 0 +hh:mm:ss IP (tos 0x0, ttl 253, id 0, offset 0, flags [DF], proto TCP (6), length 60) + 10.0.0.2.bgp > 10.0.0.1.xxx: Flags [S.], cksum 0x5dd6 (correct), seq 2536172214, ack 3226540592, win 28960, options [mss 1460,sackOK,TS val 3302301 ecr 3302300,nop,wscale 9], length 0 +hh:mm:ss IP (tos 0x0, ttl 3, id 31156, offset 0, flags [DF], proto TCP (6), length 52) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [.], cksum 0x837a (incorrect -> 0xfd89), ack 1, win 58, options [nop,nop,TS val 3302301 ecr 3302301], length 0 +hh:mm:ss IP (tos 0x0, ttl 3, id 31157, offset 0, flags [DF], proto TCP (6), length 103) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [P.], cksum 0x83ad (incorrect -> 0xd68c), seq 1:52, ack 1, win 58, options [nop,nop,TS val 3302301 ecr 3302301], length 51: BGP + Open Message (1), length: 51 + Version 4, my AS 65001, Holdtime 90s, ID 1.1.1.1 + Optional parameters, length: 22 + Option Capabilities Advertisement (2), length: 20 + Route Refresh (2), length: 0 + Multiprotocol Extensions (1), length: 4 + AFI IPv4 (1), SAFI Unicast (1) + Multiprotocol Extensions (1), length: 4 + AFI IPv6 (2), SAFI Unicast (1) + 32-Bit AS Number (65), length: 4 + 4 Byte AS 65001 +hh:mm:ss IP (tos 0x0, ttl 1, id 35114, offset 0, flags [DF], proto TCP (6), length 52) + 10.0.0.2.bgp > 10.0.0.1.xxx: Flags [.], cksum 0xfd57 (correct), ack 52, win 57, options [nop,nop,TS val 3302301 ecr 3302301], length 0 +hh:mm:ss IP (tos 0x0, ttl 1, id 35115, offset 0, flags [DF], proto TCP (6), length 103) + 10.0.0.2.bgp > 10.0.0.1.xxx: Flags [P.], cksum 0xd357 (correct), seq 1:52, ack 52, win 57, options [nop,nop,TS val 3302301 ecr 3302301], length 51: BGP + Open Message (1), length: 51 + Version 4, my AS 65002, Holdtime 90s, ID 2.2.2.2 + Optional parameters, length: 22 + Option Capabilities Advertisement (2), length: 20 + Route Refresh (2), length: 0 + Multiprotocol Extensions (1), length: 4 + AFI IPv4 (1), SAFI Unicast (1) + Multiprotocol Extensions (1), length: 4 + AFI IPv6 (2), SAFI Unicast (1) + 32-Bit AS Number (65), length: 4 + 4 Byte AS 65002 +hh:mm:ss IP (tos 0x0, ttl 3, id 31158, offset 0, flags [DF], proto TCP (6), length 52) + 10.0.0.1.xxx > 10.0.0.2.bgp: Flags [.], cksum 0x837a (incorrect -> 0xfd23), ack 52, win 58, options [nop,nop,TS val 3302301 ecr 3302301], length 0 +hh:mm:ss IP (tos 0x0, ttl 1, id 35117, offset 0, flags [DF], proto TCP (6), length 52) + 10.0.0.2.bgp > 10.0.0.1.xxx: Flags [.], cksum 0x837a (incorrect -> 0xfcf4), ack 71, win 57, options [nop,nop,TS val 3302311 ecr 3302301], length 0 +...(snip)... +``` |