Cisco BGP

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Border Gateway Protocol (RFC 4271) är ett path vector routing protokoll. Det kommunicerar på TCP port 179 så routing måste vara på plats, man kan nästan se det som ett L4-protokoll. BGP kan få många vägar till samma destination. Bästa vägen väljs utifrån en algoritm. http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

States

TCP

Idle State

ConnectRetry timer 120 sekunder

Active State

BGP speaker försöker nå peer med TCP

Connect State

TCP session established

BGP

OpenSent State

BGP version, AS number, hold time, BGP ID
Börja skicka keepalives

OpenConfirm State

Response recieved

Established State

Skicka uppdateringar
Neighbor up

Konfiguration

router bgp [ASN]
no auto-summary
router-id [loopback-adress]

Best practice

ip bgp community new-format

iBGP eller eBGP

neighbor 1.1.1.1 remote-as 65001
neighbor 1.1.1.1 description Other side
neighbor 1.1.1.1 password 7 110B1E15

Addess family

address-family ipv4
 network 10.0.0.0
 redistribute isis level-2
 neighbor 1.1.1.1 activate
 neighbor 1.1.1.1 send-community both
exit-address-family

Loopback. When configuring iBGP always use loopbacks (advertised by your IGP) for peering.

neighbor [ip-address] update-source [interface]

eBGP om det ej är directly connected, t.ex. loopback

neighbor [ip-address] ebgp-multihop 2
neighbor [ip-address] next-hop-self

Nätverk som ska annonseras

network [ip-address] mask [subnet-mask]

Standard och extended

neighbor [ip-address] send-community both

Preference

bgp default local-preference 100

Synchronization is enabled by default in Cisco IOS Software Release prior to 12.2(8)T.

no synchronization

Timers

tim bg 10 30 20

För att byta från NLRI-format till AFI-format i konfigurationen

bgp upgrade-cli

Route Reflector

Routes lärda av iBGP skickas ej vidare till iBGP-grannar per default. En route reflector bryter denna regel.
Route Reflector:

address-family ipv4
neighbor [ip-address] route-reflector-client

Dampening

route-map selective_dampening permit 10
set dampening 5 1900 2000 10

5=half-life, 1900=reuse-limit, 2000=suppress-limit, 10 max-suppress-limit

router bgp [ASN]
bgp dampening route-map selective_dampening

Route flap

show ip bgp flap-statistics

Show

show ip bgp summary
show ip bgp neighbor
show ip bgp rib-failure

Reset

clear ip bgp *
clear ip bgp <address> soft