Tài liệu BGP pdf

BGP

Key Commands Shows and Debugs

Router bgp 200 <- 200 is the AS number
Network 20.1.0.0 MASK 255.255.0.0

Neighbor 10.1.1.1 remote-as 100 <- EBGP peer
Neighbor 20.1.1.1 remote-as 200 <- IBGP peer
Aggregate-address 20.0.0.0 255.0.0.0 as-set

Neighbor 10.1.1.1 route-reflector-client
Neighbor 10.1.1.1 next-hop-self
Neighbor 10.1.1.1 ebgp-multihop

Confederations
router bgp 6001
bgp confederation identifier 666
bgp confederation peers 6002 6003
neighbor 171.69.232.55 remote-as 6002
neighbor 171.69.232.56 remote-as 6003
neighbor 160.69.69.1 remote-as 777

neighbor 10.1.1.1 update-source loopback 0
For IBGP peers only, selects loopback as source int.
Good for robustness.
Show ip bgp summary
Show ip bgp
Show ip bgp neighbor
Debug ip bgp events
Debug ip bgp updates

Clear ip bgp *
Show ip bgp filter-list
Show ip bgp paths

Communities:
Router bgp 100
neighbor 171.69.232.50 remote-as 200
neighbor 171.69.232.50 send-community
neighbor 171.69.232.50 route-map set-community out
route-map set-community 10 permit
match address 1
set community no-export
route-map set-community 20 permit
match address 2

Additional Commands

Local pref manipulation:
Access-list 1 permit 10.0.0.0 0.255.255.255
Route-map setlocalpref permit 10
Match ip address 1
Set local-preference 200
Route-map setlocalpref permit 20
Set local-preference 100
Neighbor 193.1.1.1 route-map setlocalpref in

MED:
Access-list 1 permit 10.0.0.0 0.255.255.255
Route-map setmed permit 10
Match ip address 1

Set metric 10
Route-map setmed permit 20
Set metric 50
Neighbor 193.1.1.1 route-map setmed in

Aggregate-address 160.0.0.0 255.0.0.0

Regular expressions:
. matches any single character
* matches 0 or more sequence of a given pattern
.* match any pattern
^ beginning of a string
$ end of a string
_ beginning of a string, end of string or delimiter
(space, comma)

ip as-path access-list 1 deny _300$
ip as-path access-list 1 permit .*

neighbor 10.1.1.1 filter-list 1 out

or in attribute manipulation:
route-map setlocal permit 10
match as-path 1
set local-preference 100
…

Spot The Issue Notes
• IBGP peers MUST be fully meshed, or otherwise
must use a route-reflector or confederation

• EBGP peers must be directly connected,
otherwise must use ebgp-multi-hop
• Next hop reacheability does not change within
the AS. Therefore, IBGP must be able to reach
the next hop, route normally learned via IGP.
Otherwise, use next-hop-self at the AS border
• TURN ON "NO SYNC" IN THE AS, otherwise will
need to redistribute BGP into the IGP
• Distribute-list in and out are applied with a
NEIGHBOR STATEMENT!! IOS will let you apply
a normal "distribute-list 1 in serial 0" but
it won't do squat!





Golden Rule: Never advertise a router that you
don't know how to get to. Use "show ip route"
and "show ip bgp" to compare BGP advertisements
and posted routes. Check next-hop-reacheability

localpref, weight are applied on incoming or EBGP
connections. MED is applied on outgoing EBGP
connections.

Highest local preference wins. In AS only.
Lowest MED wins. Inter AS only.

Standard communities:

Internet: advertise to all routers
No-export: do not advertise to EBGP peers
No-advertise: do not advertise to any peers
(internal or external)
local-as: Adv to IBGP or confederation peers