Workbook mistake (?) in RIP

Hi guys,

Anyone can help to confirm this for me:

 

1. RIPv2 Filtering with Prefix Lists:

 

  • Using a prefix-list, configure R5 to filter any IPv4 updates received inbound from R4 over the DMVPN cloud.
  • Solution : ip prefix-list NOT_FROM_R4 seq 5 deny 155.1.0.4/32
  • R4 IPv4 address is 155.1.0.4 /24. Will the prefix list match this? I was under the assumption 155.1.0.4/32 in prefix list means exact match 155.1.0.4 and subnet mask has to be 255.255.255.255. Thus, it will not match 155.1.0.4 /24?
        From Brian's blog:

        “ip prefix-list LIST permit 1.2.3.0/24″ would be an exact match for the prefix 1.2.3.0 with a subnet mask of 255.255.255.0. This does not match 1.2.0.0/24, nor does it match 1.2.3.4/32, nor anything in between.








2. RIPv2 Filtering with Extended ACL:


  • Configure an extended access-list filter on R5 so that routes for VLAN 7 and VLAN 9 are accepted only from R1:
    • additionally, routes to R1’s Loopback0 and VLAN 146 are accepted only from R3.
  • Solution :
    • access-list 100 deny ip host 155.1.0.3 host 155.1.7.0
    • access-list 100 deny ip host 155.1.0.3 host 155.1.9.0
  • Shouldn't it be 155.1.7.0 0.0.0.255 and 155.1.9.0 0.0.0.255 ?


Cheers.

Andy

Comments

  • Hey MartinL,

    Yeah I noticed that was a "gateway" command.

     

    From Cisco:

    gateway prefix-list-name:

    (Optional) Name of the prefix list to be applied to the gateway of the prefix being updated.

     

    So I was under the assumption it is subjected to general prefix list rule means, 155.1.0.4/32 it will ONLY match 155.1.0.4 255.255.255.255. However it's coming from 155.1.0.4 255.255.255.0. Does this matter?

  • I see. So it's smart enough to know with keyword "gateway" it'll ignore the "normal" prefix-list rule.

    Thanks.

     

    How about #2.. Any idea on it?

    Also, in regards with prefix list, is it possible to match exactly an IP address? I'm asking for prefixes though not with gateway keyword.

     

     

  • I think I am getting confused.  

    Because what I have in my head is:

     

    If I have an interface of, let's say, Gigabit1.146 with IP address of 155.1.146.4 255.255.255.0, and I want to match it exactly, I always think I can't use 

    ip prefix-list seq 10 permit 155.1.146.4/32 because it's subnet mask is not /32. 

     

    Apologies if I'm making things complicated.

  • Thanks mate. 

    Good to have my confusion cleared. 

    Cheers.

  • Yeah, I saw several other examples on other sites. So it's not a typo then. 

    I was wondering, if I use 155.1.7.0 0.0.0.255 would they dock my points? I guess I'll worry about it closer to the exam day

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