- https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/irg-route-server.pdf
- https://tools.ietf.org/html/rfc7947
Router Server = Internet Exchange (IX) Route Server = eBGP RR
- Used in internet exchange
- eBGP RR, so no need a full mesh eBGP peering among all parties
- Reduces configuration complexity and CPU/memory overhead on border routers
Requirements:
- AS_PATH transparency:
- RS doesn't append its own AS# in the AS_PATH
- RS-client doesn't enforce first AS
- Nexthop transparency:
- doesn't change NRLI's NH
- MED transparency:
- doesn't change path MED
- Path hiding:
- Per RFC 4271, BGP only advertises the best path, and a later update will be considered as an implicit withdrawal of the existing path.
- In RFC 7947, it does mention the "path hiding". So the RS only advertises the best path, which could slow down the convergence time
EOS configurations:
service routing protocols model multi-agent << must multi-agent
!
route-map rtmap-no-change-med permit 10
set metric +0 << keep metric unchanged
!
router bgp 10
router-id 10.255.255.251
neighbor RS-Client peer group
neighbor RS-Client next-hop-unchanged << NH unchanged
neighbor RS-Client as-path prepend-own disabled << no own as#
neighbor RS-Client route-map rtmap-not-change-med out << rtmap
neighbor RS-Client password 7 xLcnzAMGHkI=
neighbor RS-Client send-community
neighbor RS-Client maximum-routes 12000
neighbor 10.10.10.11 peer group RS-Client
neighbor 10.10.10.11 remote-as 11
!
How many prefixes received? Considering the following scenario:
- 3 peers advertising ONE prefix
- 2 route servers
- And all 3 peers also have bilateral peering
- Then should be 5
Router1.15:19:15#sh ip bgp 11.111.1.1
BGP routing table information for VRF default
Router identifier 180.255.255.1, local AS number 65100
BGP routing table entry for 11.111.1.1/32
Paths: 5 available
12 111
10.10.10.12 from 10.10.10.12 (10.255.255.12) << from R2
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP head, ECMP, best, ECMP contributor
Rx SAFI: Unicast
11 111
10.10.10.11 from 10.10.10.11 (10.255.255.11) << from R1
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor
Rx SAFI: Unicast
11 111
10.10.10.11 from 10.10.10.251 (10.255.255.251) << R1 vis RS1
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor
Rx SAFI: Unicast
11 111
10.10.10.11 from 10.10.10.252 (10.255.255.252) << R1 via RS2
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor
Rx SAFI: Unicast
13 333 111
10.10.10.13 from 10.10.10.13 (10.255.255.13) << R3
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external
Rx SAFI: Unicast
Let's shut down the private peering to R2. So you can see the RS1 and RS2 don't advertise R2's path.
Router.15:26:31(config-router-bgp)#sh ip bgp 11.111.1.1
BGP routing table information for VRF default
Router identifier 180.255.255.1, local AS number 65100
BGP routing table entry for 11.111.1.1/32
Paths: 4 available
11 111
10.10.10.11 from 10.10.10.252 (10.255.255.252) << RS2
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external, best
Rx SAFI: Unicast
11 111
10.10.10.11 from 10.10.10.251 (10.255.255.251) << RS1
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external
Rx SAFI: Unicast
11 111
10.10.10.11 from 10.10.10.11 (10.255.255.11) << R1
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external
Rx SAFI: Unicast
12 111
10.10.10.12 from 10.10.10.12 (10.255.255.12) << R2
Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external
Rx SAFI: Unicast
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