====== Cisco BGP ======
see also: **[[:networking]]**, **[[:cisco]]**, **[[http://www.cymru.com/Documents/secure-bgp-template.html|Secure BGP template for Cisco]]**

----
commands:

//closes bgp sessions//
  clear ip bgp *
[[http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/1cdbgp.htm#wp1002274]]

**Please write more coments on configurations!!**

  router bgp 15393
   no synchronization
   bgp dampening
   neighbor customer-pg peer-group
   neighbor customer-pg route-map customer-rm in
   neighbor customer-pg route-map standardout out
   neighbor X.X.X.A peer-group customer-pg
   neighbor X.X.X.A remote-as 65502
   neighbor X.X.X.A filter-list 100 in
   neighbor X.X.X.A distribute-list 100 in
  !
  ! as-path filter to catch peers announcements
  no ip as-path access-list 100
  ip as-path access-list 100 permit _(65502)$
  ! acl to catch adverts for peers address space
  no access-list 100
  access-list 100 permit ip 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0
 
  ! acl to catch adverts for sub-aggregates of own address space
  no access-list 199
  access-list 199 permit ip X.X.X.0 0.0.31.255 255.255.240.0 0.0.15.255
  ! acl to catch adverts for own address space
  no access-list 97
  access-list 97 permit X.X.X.0 0.0.31.255

  ! acl to catch adverts for bogus address space
  no access-list 98
  access-list 98 permit 10.0.0.0 0.255.255.255
  access-list 98 permit 172.16.0.0 0.15.255.255
  access-list 98 permit 192.168.0.0 0.0.255.255
  access-list 98 permit 0.0.0.0 0.255.255.255
  access-list 98 permit 127.0.0.0 0.255.255.255
  access-list 98 permit 128.0.0.0 0.0.255.255
  access-list 98 permit 191.255.0.0 0.0.255.255
  access-list 98 permit 192.0.0.0 0.0.0.255
  access-list 98 permit 223.255.255.0 0.0.0.255
  access-list 98 permit 224.0.0.0 15.255.255.255

  ! acl to catch adverts for default route
  no access-list 99
  access-list 99 permit 0.0.0.0 0.0.0.0
  route-map customer-rm deny 10
   match ip address 97 98 99

  route-map customer-rm permit 20
  set local-preference 150

  route-map standardout deny 10
   match ip address 98 99 199
  route-map standardout permit 20


===== Useful commands =====
FIXME - styling (and more detailed)

   Router# show ip bgp nei 172.16.0.2 received-routes

and 

   Router# show ip bgp nei 172.16.0.2 routes

and

   Router# show ip bgp rib-failure

===== Preventing AS from becoming Transit AS =====

To prevent your AS from becoming a Transit AS, use following startegy
Create a route map say ''“transit”'' in config mode

   route-map transit permit 10
   match as-path 1

In config mode, use following command

   ip as-path access-list 1 deny ^$

This command will only allow routes with origin code “''i''” and filter all routes with incomplete as-path.
Apply the above route-map  with neighbor statement

   router bgp 64000
   neighbor 2.2.2.2 route-map transit in

Only routes with origin code” i” will enter your AS.

===== AS-path prepending =====
   router bgp 65001
     neighbor 10.1.0.2 remote-as 65200
     neighbor 10.1.0.2 description Backup ISP
     neighbor 10.1.0.2 route-map prepend out
    !
    route-map prepend permit 10
    set as-path prepend 65001 65001 65001


===== Extracting BGP info with regular expressions =====

**Short version:**
   show ip bgp regexp [AS]$ - list all network paths with that AS
   show ip bgp regexp _AS_ - match any route going through AS
   show ip bgp regexp _AS AS_ - match any route passed through AS and AS
   show ip bgp regexp _AS$ - match only routes originated in this AS

To find all subnets originating from AS 100 (AS path ends with 100): \\
\\
''**Router# show ip bgp regexp _100$**''
   ...
      Network          Next Hop            Metric LocPrf Weight Path
   *  10.1.0.0/30      172.16.0.6                             0 300 100 ?
   *>                  172.16.0.1               0             0 100 ?
   *  172.16.0.0/30    172.16.0.6                             0 300 100 ?
   *                   172.16.0.1               0             0 100 ?
   ...

To find all subnets reachable via AS 100 (AS path begins with 100):\\
\\
**''Router# show ip bgp regexp ^100_''**
   ...
      Network          Next Hop            Metric LocPrf Weight Path
   *> 10.1.0.0/30      172.16.0.1               0             0 100 ?
   *  10.3.0.0/30      172.16.0.1                             0 100 300 ?
   *  172.16.0.0/30    172.16.0.1               0             0 100 ?
   *> 172.16.0.8/30    172.16.0.1               0             0 100 ?
   ...

To find all routes traversing AS 100:\\
\\
**''Router# show ip bgp regexp _100_''**
   ...
      Network          Next Hop            Metric LocPrf Weight Path
   *  10.1.0.0/30      172.16.0.6                             0 300 100 ?
   *>                  172.16.0.1               0             0 100 ?
   *  10.3.0.0/30      172.16.0.1                             0 100 300 ?
   *  172.16.0.0/30    172.16.0.6                             0 300 100 ?
   ...

If you need to further filter the output, use quote-regexp instead. For example, to find all 172.x.x.x routes originating from AS 100: \\
\\
''**Router# show ip bgp quote-regexp "_100$" | include ^.  172\.**''
    ...
    *  172.16.0.0/30    172.16.0.6                             0 300 100 ?
    *  172.31.0.1/32    172.16.0.6                             0 300 100 ?

Or, to find all subnets currently being reached via AS 100: \\

**''Router# show ip bgp quote-regexp "^100_" | i ^.>''** 
    ...
    *> 10.1.0.0/30      172.16.0.1               0             0 100 ?
    *> 172.16.0.8/30    172.16.0.1               0             0 100 ?
    *> 172.31.0.1/32    172.16.0.1               0             0 100 ?