BGP -prefix-list route-map problem.

Unanswered Question
May 22nd, 2010

Hi,

We are receiving three subnets from external BGP peer next hop  10.1.2.1 expernal BGP peer ID

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

R6#sh ip bgp

BGP table version is 16, local router ID is 1.1.6.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 0.0.0.0          1.1.3.1                  0             0 11 i

*> 172.16.10.0/24   1.1.3.1                  0             0 11 i

*> 192.168.1.0      1.1.3.1                  0             0 11 i

Here is the pre-fix list and route map configured

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

ip prefix-list fromr3 seq 5 permit 192.168.1.0/24

route-map fromr3 permit 10

match ip address fromr3

set local-pref 110

  set as-path prepend 11 11 11 11

!

route-map fromr3 permit 20

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} # neighbor 1.1.3.1 route-map fromr3  in   Route map applied "in" direction.

With this configuration only subnet  192.168.1.0/24 is expected to have prepended by 11 11 11.

Remaining subnets are passed on the the second statement which will be passed on without any change in any attributes.


But what was found is it is prepending all routes with 11 11 11 and also Loc_pref 110. Here is the output

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

R6#sh ip bgp

BGP table version is 4, local router ID is 1.1.6.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 0.0.0.0          1.1.3.1                  0    110      0 11 11 11 11 11 i

*> 172.16.10.0/24   1.1.3.1                  0    110      0 11 11 11 11 11 i

*> 192.168.1.0      1.1.3.1                  0    110      0 11 11 11 11 11 i

Why is this taking place?

Please share the experience

Thanks

Subodh

I have this problem too.
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Reza Sharifi Sat, 05/22/2010 - 19:56

Hi Subodh,

To resolve this issue you need to change "match ip address fromr3"

to "match ip address prefix-list fromr3"

Remember you defined a prefix-list and you have to reference that in your route-map.

Also do not forget "cle ip bg

HTH

Reza

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