netdev - Re: specifying scopid's for link-local IPv6 addrs

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Date:	Tue, 24 Jul 2007 10:28:31 -0700
From:	Sridhar Samudrala <sri@...ibm.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Bill Fink <billfink@...dspring.com>,
	Linux Network Development list <netdev@...r.kernel.org>
Subject: Re: specifying scopid's for link-local IPv6 addrs

On Tue, 2007-07-24 at 10:13 -0700, Rick Jones wrote:
> > Rick,
> > 
> > I don't see any way around this.  For example, on one of my test
> > systems, I have the following link local routes:
> > 
> > chance% netstat -A inet6 -rn | grep fe80::/64
> > fe80::/64                                   ::                                      U     256    0        0 eth0
> > fe80::/64                                   ::                                      U     256    0        0 eth2
> > fe80::/64                                   ::                                      U     256    0        0 eth3
> > fe80::/64                                   ::                                      U     256    0        0 eth4
> > fe80::/64                                   ::                                      U     256    0        0 eth5
> > fe80::/64                                   ::                                      U     256    0        0 eth6
> > 
> > So if I want to run a link local test to fe80::202:b3ff:fed4:cd1,
> > the system has no way to choose which is the correct interface to
> > use for the test, and will give an error if the interface isn't
> > specified. 
> 
> Yeah, I was wondering about that.  I'm not sure if the attempts on "those other 
> OSes" happened to involve multiple interfaces or not.  Even so, it "feels" 
> unpleasant for an application to deal with and I wonder if there is a way for a 
> stack to deal with it on the application's behalf.  I guess that might involve 
> some sort of layer violation between neightbor discovery and routing (typing 
> while I think about things I know little about...)
> 
> Is there RFC chapter and verse I might read about routing with multiple 
> link-local's on a system?
> 
> > You must explicitly specify the desired interface.  For example,
> > on my test system, the correct interface is eth6 which is interface 8
> > (lo eth0 eth1 eth2 ... eth5 eth6).  Here is an example nuttcp test
> > specifying interface 8:
> > 
> > chance% nuttcp -P5100 fe80::202:b3ff:fed4:cd1%8
> >  1178.5809 MB /  10.02 sec =  986.2728 Mbps 12 %TX 15 %RX
> > 
> > nuttcp uses getaddrinfo() which parses the "%<ifindex>" field,
> > and then copies the sin6_scope_id from the res structure to the
> > server's sockaddr_in6 structure before initiating the connect().
> 
> OK, I'll give that a quick try with netperf:
> 
> [root@...pc106 ~]# netperf -H 192.168.2.107 -c -C -i 30,3 -- -s 1M -S 1M -m 64K 
> -H fe80::207:43ff:fe05:9d%2

We can even specify the interface name instead of the interface index
   <link-local>%ethX

getaddrinfo() uses if_nametoindex() internally to get the index.

Thanks
Sridhar
> TCP STREAM TEST from ::0 (::) port 0 AF_INET6 to fe80::207:43ff:fe05:9d%2 
> (fe80::207:43ff:fe05:9d) port 0 AF_INET6 : +/-2.5% @ 99% conf.
> 
> Cool - it establishes the data connection just fine.
> 
> 
> To further demonstrate my ignorance :)  is that %n suffix something one might 
> expect in most/all getaddrinfo()'s or is that unique to the one in Linux?
> 
> rick jones
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