prefix & AS-path questions

From: Gary Bartlett (ciscokid@sympatico.ca)
Date: Thu Sep 11 2003 - 10:49:45 GMT-3


So it's coming down to the wire for me now, I'll be taking the exam on
Sept 18th in RTP. There are still a few things I'm not comfortable with,
so if you could help me with these I'd appreciate it.
Thanks,
Gary
 
1. Construct a route map that sets the BGP local preference to 200 for
any paths learned directly from AS 307, sets the local pref to 400 for
any paths learned directly from AS 698 that pass through AS 405, and
denies all other paths.
2. Construct a route map that:
- Sets the origin code to "incomplete" and the local preference to 50
for the 10.0.0.0/8 network and any of its subnets.
- Sets the weight to 10,000 and the local preference to 60 for networks
in the range 172.16.0.0/16 to 172.31.0.0/16 network, and any of their
subnets.
- Sets the local preference to 70 for any 192.168.x.0/24 network or
subnet.
- Denies all other prefixes.
 
MY ANSWERS
1)
route-map ex1 permit 10
 match as-path 11
 set local-preference 200
route-map ex1 permit 20
 match as-path 12
 set local-preference 400
ip as-path access-list 11 permit ^307_
ip as-path access-list 12 permit ^698_(.+_)*405_(.+_)$
-------------------------
 
2)
route-map ex2 permit 10
 match ip address prefix test21
 set origine incomplete
 set local-preference 50
route-map ex2 permit 20
 match ip address prefix test22
 set weight 10000
 set local-preference 60
route-map ex2 permit 30
 match ip address prefix test23
 set local-preference 70
ip prefix-list test21 seq 5 permit 10.0.0.0/8 le 32
ip prefix-list test22 seq 5 permit 172.16.0.0/12 ge 16 le 32
----------------------
ip prefix-list test23 seq 5 permit 192.168.0.0/16 le 32
 
COMMENTS:
1) My problem is that they said passed through as 405, but they didn't
say originated from AS 405, that's why my answer is different...
2) I added ge 16 because in the question they said that the 3rd octet
could be any # in the range of 16 to 31, but the subnet would still be
/16 to /32...
THERE ANSWERS
1.
 route-map test1 permit 10
  match as-path 1
  set local preference 200
 route-map test1 permit 20
  match as-path 11
  set local preference 400
 
 ip as-path access-list 1 permit ^307_
 ip as-path access-list 11 permit ^698_(.+_)*405_ -----------------
2.
 route-map test2 permit 10
  match ip address prefix test2a
  set origin incomplete
  set local-preference 50
 route-map test2 permit 20
  match ip address prefix test2b
  set weight 10000
  set local-preference 60
 route-map test2 permit 30
  match ip address prefix test2c
  set local-preference 70
 ip prefix-list test2a seq 5 permit 10.0.0.0/8 le 32
 ip prefix-list test2b seq 5 permit 172.16.0.0/12 le 32
----------------
 ip prefix-list test2c seq 5 permit 192.168.0.0/16 le 32



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