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18290 Views 17 Replies Latest reply: May 21, 2009 11:33 PM by Conwyn RSS 1 2 Previous Next

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RIP V2 and multicast

May 21, 2009 11:07 AM

Eric Belrose 180 posts since
Jun 27, 2008

I was doing Lab 21 on the CCENT simulator from ciscopress.  I noticed on debug ip rip that the updates were being sent to the lan segment.  I know that rip is enabled on that network, however in the lab there are 2 routers, 2 switches, and two PCs.  The two routers are linked together and the switches to the routers, PCs to the switches 1 each.

 

I dont understand why R1 would send the update using version 2 through the LAN when there shouldn't be any subscribers to the multicast group unless the switch is a L3 switch, it wouldn't join that multicast group and the router shouldn't forward.  I know that I still need to go further in my development but this is my understanding.

 

Am I correct on this or does RIP Version 2 automatically send to all networks (out all interfaces with networks configured) regardless of IGMP joins for a multicast group?

  • Krzysztof Przybylski 64 posts since
    May 8, 2009
    Currently Being Moderated
    1. May 21, 2009 11:34 AM (in response to Eric Belrose)
    Re: RIP V2 and multicast

    Hi,

     

     

    To avoid tranmitting ro updates, you can configure passive-interface on ethernet connection ( from router level configuration).

    Passive int will only allow to receive routing updates.

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,395 posts since
    Oct 7, 2008
    Currently Being Moderated
    2. May 21, 2009 12:05 PM (in response to Eric Belrose)
    Re: RIP V2 and multicast

    Routing updates work with 224.0.0.x which is link-local multicast.  There is no IGMP join for link-local groups!

     

    You send updates out to any "enabled" interface.  You can verify these with "show ip protocols" but the short answer is that any interface covered in the range of IPs within your "network" command is enabled.

     

    As another poster said, use the "passive-interface" to help.  Or better yet, "passive-interface default" which turns off updats on ALL interfaces.  You need to specifically configure and want updates on specific interfaces then.  So it forces you to pay attention to where or where not the updates go.

     

    Cheers,

     

    Scott

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    Re: RIP V2 and multicast

    Hi Scott

     

    You slipped in before me. I was going to cite this from the text below.

    Note It is not necessary to configure Internet Group Management Protocol (IGMP) because the periodic broadcasts are interrouter messages that are not forwarded

    Regards Conwyn

    ip rip v2-broadcast

    To allow Routing Information Protocol (RIP) Version 2 update packets to be sent as broadcast packets instead of multicast packets, use the rip v2-broadcast command in interface configuration mode. To disable the broadcast of IP RIP Version 2 update packets that are sent as broadcast packets, use the no form of this command.

    ip rip v2-broadcast

    no ip rip v2-broadcast

    Syntax Description

    This command has no arguments or keywords.

    Defaults

    This command is disabled by default. Unless the ip rip v2-broadcast commend is entered, RIP Version 2 update packets are sent as multicast packets.

    Command Modes

    Interface configuration

    Command History

    Release
    Modification

    12.1(5)T

    This command was introduced.

     

    Usage Guidelines

    Use the ip rip v2-broadcast command to broadcast RIP Version 2 broadcast updates to hosts that do not listen to multicast broadcasts. Version 2 updates (requests and responses) will be sent to the IP broadcast address 255.255.255.255 instead of the IP multicast address 244.0.0.9.

    In order to reduce unnecessary load on those hosts that are not listening to RIP Version 2 broadcasts, the system uses an IP multicast address for periodic broadcasts. The IP multicast address is 244.0.0.9.


    Note It is not necessary to configure Internet Group Management Protocol (IGMP) because the periodic broadcasts are interrouter messages that are not forwarded.

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    5. May 21, 2009 12:20 PM (in response to Eric Belrose)
    Re: RIP V2 and multicast

    Hi Eric

     

    Normally passive interface will not send anything what ever you code on the interface so if you use passive-interface default then it will not send but I believe a RIP passive interface still receives updates. Scott to confirm.

     

    Regards Conwyn

  • Currently Being Moderated
    6. May 21, 2009 3:25 PM (in response to Eric Belrose)
    Re: RIP V2 and multicast

    Hi!

     

    Be careful with the passive-interface default command when using with routing protocols that use hellos to form adjacencies.  This will probably cause some undesired results if not used with caution.  Just a simple thought.

     

    Erick

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,395 posts since
    Oct 7, 2008
    Currently Being Moderated
    7. May 21, 2009 3:50 PM (in response to Erick)
    Re: RIP V2 and multicast

    Undesirable results?  As in you have to make sure you WANT particular interfaces enabled?  Security...  no surprises...   I dunno, I've never been surprised by anything with using the default.  Other than my own lack of paying attention and forgetting to enable it. 

     

    But to answer a previous question, changing your "ip rip send" or "ip rip receive" information will NOT override the passive interface functionality.

     

    HTH,

     

    Scott

  • Currently Being Moderated
    Re: RIP V2 and multicast

    I would expect a response like this from a quad CCIE, however I was addressing a question regarding CCENT level knowledge, which as it is, passive-interface command is NOT a part of this level of understanding.

     

    I think it is important to meet our posters at the level of understanding they have.  C'mon guys,  Passive-interface command?  That's not really discussed until CCNP with regards to controlling routing updates.  This posters was clear in telling us he was doing a CCENT lab.

     

    If someone is explicit in stating they are doing CCENT level labs, let's not confuse them with CCNP level material.  In the end that will confuse them even more and shift them away from focusing on whats important to be able pass the CCENT exam.

     

    Cheers

     

    Erick

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,395 posts since
    Oct 7, 2008
    Currently Being Moderated
    9. May 21, 2009 4:30 PM (in response to Erick)
    Re: RIP V2 and multicast

    heheheh..  Fair enough.  Although I'm pretty sure that passive-interface is in the beginning stages of configurations.  While it may not be CCENT, I'm relatively sure it's within the CCNA parameters.

     

    At least it's in some CCNA labs I've reviewed in the past.  *shrug*

     

    Scott

  • Currently Being Moderated
    Re: RIP V2 and multicast

    Scott,

     

    No doubt.  I am sure it's mentioned in the CCNA (ICND2) material, but it is not something that is detailed or mentioned as something that should be learned for the CCNA exam.   I am sorry if you felt as though it was an attack on your post or whatever.  I was addressing the original poster and to give him a heads on if he used that command with a link-state routing protocol or EIGRP in his home lab.

     

      You seem to be pretty defensive in nature.  Maybe that's just my perspective.    Maybe because someone had the guts to challenge your thinking.  Who knows.

     

    I truly have a passion for helping people who are studying for the CCENT/CCNA exam.  I remember how much time and dedication it took to acheive my goal.  I want to try and help with all my heart and I am just trying to keep the level of knowledge mentioned by the original poster in perspective with what he is studying.

     

    Cheers

     

    Erick

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,395 posts since
    Oct 7, 2008
    Currently Being Moderated
    13. May 21, 2009 6:52 PM (in response to Erick)
    Re: RIP V2 and multicast

    I never really thought of myself as defensive before...  But ok.  Sorry if I came off that way.   Anyone may feel free to challenge my posts.  I am most certainly not omniscient nor omnipotent.  Last I checked, I have not been promoted to a minor deity status.

     

    I rather thought the idea was a discussion, but my apologies if I offended.  And while I can understand your concept of wanting to help those for the CCENT/CCNA exam, my only word of caution would be that it's not necessarily a "required" move to filter out information to only target an exam.  I've never been fond of the exam-based certification books for that reason.  There are often gaps of knowledge.  When you culminate the CCENT, CCNA and CCNP "test topics" and then  try to go towards CCIE there are some large gaps in knowledge.  Sometimes those gaps are very basic in nature, but it's due to what specific things are highlighted.

     

    IMHO, aim higher.  If you know more than what's required, you should be able to pass the tests without difficulty.  But I certainly understand the opinion of it, and didn't mean to come across as defensive or abrassive.

     

    Cheers,

     

    Scott

  • Currently Being Moderated
    14. May 21, 2009 6:55 PM (in response to Eric Belrose)
    Re: RIP V2 and multicast

    It's all good.  When you mention the passive-interface command, that is not something that is generally discussed in great detail for CCENT or CCNA candidates.  I am not saying it's not MENTIONED.  I am just saying that s not something that is truly discussed in great detail until the CCNP level.

     

    As for the post in which I addressed Scott, his contention with me has to do with something discussed in a previous post and I feel his contention is rearing it's ugly head in your post.  Sorry about that. 

     

    If there is anything else I might be able to help with just let us know.  We are all here to help to any degree we can.  We aren't all quad CCIE's and I can speak for myself that I will probably not be, but most people here know what they are talking about if they decicde to respond to a post even if we don't have CCIE # by our name.

     

    Erick

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