[Xorp-users] Using Xorp for PIM SSM

Bruce Simpson bms at incunabulum.net
Tue Jun 2 08:11:40 PDT 2009


Hi,

Thanks for your question regarding XORP's PIM-SM implementation.

pcaldes wrote:
> ...
> We figure we should be able to run Xorp on one of the servers and it can 
> convert IGMPv3 to PIM
> for other servers on the VLAN in addition to an IGMPv3 application on 
> the same box
>   

I believe that should work. I should point out that XORP does not 
currently support IGMP proxy mode functionality, so if you intend to use 
XORP as the multicast topology intermediate hop, running PIM-SM is the 
only option supported.

...
>                                              
>
> The Xorp router only needs to support SSM so no RP should be needed but 
> we cannot get it to work.
> Hopefully it is just a configuration error.
>   

I believe this is a limitation of the configuration options for XORP's 
PIM-SM implementation. Not knowing the inner workings in detail, I can't 
say for sure -- I believe it assumes engineers will be deploying both 
ASM and SSM models, therefore an RP is required.

A static RP configuration should be fine, providing it doesn't clash 
with an existing RP in the PIM-SM domain.

> We know our applications send out IGMPv3 SSM joins since if we stop Xorp
> and enable IGMPv3 on the Cisco router, everything works.
>
> Also, is there a configuration command similar to Cisco's "ip pim ssm 
> range" statement which allows
> you to specify non-standard SSM subnet ranges?
>
>   

Unfortunately no, I believe this is a limitation of the current 
implementation for much the same reasons.  I am sure this functionality 
can be added given xorp_pim's decent C++ abstractions.

> Before we start XORP, we make sure to run:
>
>     echo 0 > /proc/sys/net/ipv4/conf/eth0/rp_filter
>   

Just as an aside: I see this is recommended in the XORP User Manual.

I believe this is conceptually similar to FreeBSD's 
net.inet.ip.check_interface feature, however I believe Linux doesn't 
fully implement the RFC 1122 Strong End-Station model for the same 
software stack limitations as FreeBSD has.   I'd be curious to know why.
  
>
>
> Can you please look over my config file for any mistakes?
> All help is appreciated.
>   

Your configuration looks OK, apart from the fact that there is no 
cand-rp or bootstrap blocks in the pim configuration block.

I believe that the quickest way to resolve your issue may be to just add 
a cand-rp block to the XORP configuration with a scope-zone for the SSM 
range you intend to use, even though SSM actually requires no RP, unlike 
the ASM model.

thanks,
BMS



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