Cisco BGP
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. TCP står för acknowledgement, retransmission, sequencing och update fragmentation. 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
Contents
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
Pakettyper
OPEN: Första paketet som skickas av varje sida
UPDATE: En update skickas endast en gång
NOTIFICATION: Errormeddelanden
KEEPALIVE: Skickas regelbundet
Konfiguration
För att byta från NLRI-format till AFI-format i konfigurationen
bgp upgrade-cli
Neighbors
router bgp [ASN] no auto-summary router-id [loopback-adress]
iBGP eller eBGP (ttl 1)
neighbor 1.1.1.1 remote-as 65001 neighbor 1.1.1.1 description Other side
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
Nätverk som ska annonseras
network [ip-address] mask [subnet-mask] show ip bgp 10.10.10.0/24
Soft
neighbor 1.1.1.1 soft-reconfiguration inbound
Send default route
default-information originate
Synchronization is enabled by default in Cisco IOS Software Release prior to 12.2(8)T.
no synchronization
Timers
tim bg 10 30 20
Peer Group
För att förenkla konfen kan man gruppera flera grannar i så kallade peer groups.
neighbor GROUP01 peer-group neighbor 1.1.1.1 peer-group GROUP01
Passive Peer
Dynamic Peering
Next Hop
Ändra så att annonserade uppdateringar har den egna IP-adressen istället för det som står i uppdateringen från den granne man har lärt sig nätverket av.
neighbor [ip-address] next-hop-self
NLRI
Summarization
aggregate-address, null route automatically installed
aggregate-address 10.0.0.0 255.0.0.0 [summary-only]
summary-only, suppress detailed routes
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
Communities
Best practice
ip bgp community new-format
Skicka standard och extended
neighbor [ip-address] send-community both
Show
show ip bgp community
Filtering
AS
Regular Expressions
- .* = Any
- ^$ = Local AS
ACL
ip as-path access-list 100 permit .* neighbor 1.1.1.1 filter-list 100 in
Network
access-list 1 permit 10.10.10.0 0.0.0.255 neighbor 1.1.1.1 distribute-list 1 in
AS-path manipulation
Convergence
Don't wait for the hold-down timer (180 sec) to expire.
bgp fast-external-fallover #Global ip bgp fast-external-fallover #Per interface
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 bgp ipv4 unicast show ip bgp neighbor show ip bgp paths show ip bgp rib-failure
Routes som skickas
sh ip bgp vrf Name neighbors 10.10.10.10 advertised-routes
Reset
clear ip bgp * clear ip bgp <address> soft
Debug
debug ip bgp events
MED
multi-exit discriminator
ip access-list standard MED permit 1.1.1.0 0.0.0.255 route-map MED_50 permit 10 match ip address MED set metric 50
Local Preference
Preference
bgp default local-preference 100
Högst preference vinner
route-map LOCALPREF permit 10 set local-preference 500 neighbor 1.1.1.1 route-map LOCALPREF in
BMP
The BGP Monitoring Protocol (BMP) feature supports the following functionality to monitor Border Gateway Protocol (BGP) neighbors
router bgp 65000 neighbor 30.1.1.1 bmp-activate server 1 bmp server 1 activate
Show
show ip bgp bmp server 1 show ip bgp bmp server summary
