BGP CHAPTER 11 (IP PREFIX-LIST)
QUESTION:
22. What is prefix-list ?
23. What is BGP Community ?
24: What is BGP Community Syntax ?
25a: What are different types of BGP Communities ?
SOLUTION:
22. What is prefix-list ?
. An improvement on Access lists for matching routes
- improved processor utilization
- better subnet mask matching abilities
. Two stage matching system : network + mask
Some examples:
ip prefix-list ONE permit 0.0.0.0/0 (permit default route)
ip prefix-list TWO permit 0.0.0.0/0 le 32 (permit any)
ip prefix-list THREE permit 0.0.0.0/0 ge 32 (permit all host routes)
ip prefix-list FOUR permit 0.0.0.0/1 ge 24 le 24 ( matches any class A
address with class C subnet mask)
ip prefix-list FIVE permit 128.0.0.0/2 ge 16 (match any class B with subnet
mask >= 16)
We can use prefix-list with neighbour command or with route-map to tune
attributes of BGP.
23. What is BGP Community ?
. It is BGP Route tagging method.
. Coupled with BGP policy.
New Format vs Old format:
. BGP community attribute is a 32-bit value.
- 4,294,967,295 valures
RFC 1977 took the 32 bit value and split it into two 655536 values
<AS>:<Community>
examples 500:18 or 500:99
24: What is BGP Community Syntax ?
. Use the new 16bit:16bit Community format.
router(config)# ip bgp-community new-format
. Send Communities to a neighbor (Stripped by default)
router(config-router)# neighbor <ip> send-community
. Set A community value in a route map
router(config-route-map)# ip community-list <standard|extended> <name>
Simple Community-list:
router(config)# ip community-list <1-99>
extended community-list
router(config)# ip community-list <100-199>
extended community list matches on the basis of regular expressions.
Named Community-list
router(config)# ip community-list <standard|extended> <name>
25a: What are different types of BGP Communities ?
-->
Internet(default) : all BGP routes have this community 0 (this is std bgp tag)
Local-AS : It does not advertised the routes outside the local-as.
No-export : It will not advertise outside EBGP peer , but it will communicate
on cofederation.
No-advertise: It will not advertise outside its neighbour.
None:
QUESTION:
22. What is prefix-list ?
23. What is BGP Community ?
24: What is BGP Community Syntax ?
25a: What are different types of BGP Communities ?
SOLUTION:
22. What is prefix-list ?
. An improvement on Access lists for matching routes
- improved processor utilization
- better subnet mask matching abilities
. Two stage matching system : network + mask
Some examples:
ip prefix-list ONE permit 0.0.0.0/0 (permit default route)
ip prefix-list TWO permit 0.0.0.0/0 le 32 (permit any)
ip prefix-list THREE permit 0.0.0.0/0 ge 32 (permit all host routes)
ip prefix-list FOUR permit 0.0.0.0/1 ge 24 le 24 ( matches any class A
address with class C subnet mask)
ip prefix-list FIVE permit 128.0.0.0/2 ge 16 (match any class B with subnet
mask >= 16)
We can use prefix-list with neighbour command or with route-map to tune
attributes of BGP.
23. What is BGP Community ?
. It is BGP Route tagging method.
. Coupled with BGP policy.
New Format vs Old format:
. BGP community attribute is a 32-bit value.
- 4,294,967,295 valures
RFC 1977 took the 32 bit value and split it into two 655536 values
<AS>:<Community>
examples 500:18 or 500:99
24: What is BGP Community Syntax ?
. Use the new 16bit:16bit Community format.
router(config)# ip bgp-community new-format
. Send Communities to a neighbor (Stripped by default)
router(config-router)# neighbor <ip> send-community
. Set A community value in a route map
router(config-route-map)# ip community-list <standard|extended> <name>
Simple Community-list:
router(config)# ip community-list <1-99>
extended community-list
router(config)# ip community-list <100-199>
extended community list matches on the basis of regular expressions.
Named Community-list
router(config)# ip community-list <standard|extended> <name>
25a: What are different types of BGP Communities ?
-->
Internet(default) : all BGP routes have this community 0 (this is std bgp tag)
Local-AS : It does not advertised the routes outside the local-as.
No-export : It will not advertise outside EBGP peer , but it will communicate
on cofederation.
No-advertise: It will not advertise outside its neighbour.
None:
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