Kevin Dorrell, CCIE #20765

13 Mar 2008

IOS Gotcha : section filter

Filed under: IOS features — dorreke @ 04:35

The first one is to do with the “section” filter.  I read about the “section” filter on a blog a few weeks back, and I have been using it extensively since.  It is one of the most useful features I have seen in a long time.  But you have to be careful how you interpret its output.  Let’s check the eigrp process on R2, NMC lab 11:

R2#show run | section eigrp 
router eigrp 12 
 redistribute ospf 11 route-map OSPF-->EIGRP 
 network 141.11.25.0 0.0.0.255 
 auto-summary 
 redistribute eigrp 12 subnets route-map EIGRP-->OSPF

Aaagh!  How did that happen?  When I was configuring, I must have thought I was in the OSPF section, but instead, accidentally redistributed EIGRP into itself.  I didn’t know you could do even that.  Let’s remove it:

R2#conf t 
Enter configuration commands, one per line.  End with CNTL/Z. 
R2(config)#router eigrp 12 
R2(config-router)#no redistribute eigrp 12 
redistribution of "eigrp" via "eigrp" not allowed 
R2(config-router)#

Sure.  That makes sense in itself.  But it still seems to be there: 

R2#show run | section eigrp 
router eigrp 12 
 redistribute ospf 11 route-map OSPF-->EIGRP 
 network 141.11.25.0 0.0.0.255 
 auto-summary 
 redistribute eigrp 12 subnets route-map EIGRP-->OSPF

 Gotcha!  It’s an artifact of the “section” filter.  The rogue redistribute was in the OSPF section all along.  It just happened to string-match “eigrp”.

Here is another example from the same router:

 R2#show run | section ospf 
 ip ospf network point-to-point 
 ip ospf 11 area 2 
 ip ospf network point-to-multipoint 
 ipv6 ospf 100 area 25 
 redistribute ospf 11 route-map OSPF-->EIGRP 
router ospf 11 
 router-id 141.11.102.1 
 log-adjacency-changes 
 redistribute eigrp 12 subnets route-map EIGRP-->OSPF 
 network 141.11.10.0 0.0.0.255 area 0 
 distance ospf external 180 
 redistribute ospf 100 include-connected 
ipv6 router ospf 100 
 router-id 141.11.102.1 
 log-adjacency-changes 
 redistribute connected 
 redistribute bgp 100 metric 20 
R2#

It looks like I have accidentally redistributed a non-existant OSPF 100 process into OSPF 11.  Of course (?) I haven’t.  The command in red is actually in the router BGP section under the IPv6 address-family.  Let’s try and remove it:

R2#conf t 
Enter configuration commands, one per line.  End with CNTL/Z. 
R2(config)#router ospf 11 
R2(config-router)#no redistribute ospf 100 
R2(config-router)#^Z 
R2#

That seems to have done the trick:

 R2#show run | section ospf 
 ip ospf network point-to-point 
 ip ospf 11 area 2 
 ip ospf network point-to-multipoint 
 ipv6 ospf 100 area 25 
 redistribute ospf 11 route-map OSPF-->EIGRP 
router ospf 11 
 router-id 141.11.102.1 
 log-adjacency-changes 
 redistribute eigrp 12 subnets route-map EIGRP-->OSPF 
 network 141.11.10.0 0.0.0.255 area 0 
 distance ospf external 180 
 redistribute ospf 100 include-connected 
ipv6 router ospf 100 
 router-id 141.11.102.1 
 log-adjacency-changes 
 redistribute connected 
 redistribute bgp 100 metric 20 
R2#

Oh!  It’s still there!  Duh!  Gotcha!

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2 Comments »

  1. […] (BTW, I have done another posting about the dangers of the “section” filter.) […]

    Pingback by IOS Gotcha : no redistribute eigrp 12 subnets route-map EIGRP–>OSPF « Kevin Dorrell’s CCIE Study Weblog — 13 Mar 2008 @ 05:14

  2. If you can give me any pointers to a “clear and concise” works in distribution i would appreciate it. I’ve covered EVERYTHING else in the R&S CCIE blueprint – but still can’t seem to get my head around redistribution.

    Comment by Ciscowannabe — 06 Aug 2009 @ 16:39


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