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Joachim Nilsson edited this page Jul 17, 2015 · 4 revisions

This text is taken from README.config for pimd, the PIM multicast daemon.

Using GRE Tunnels for Multicast Routing

Based on information contributed by Hiroyuki Komatsu mailto:[email protected]

If you are configuring the particular gre interfaces for first time, ignore the errors after ip link set gre1 down and ip tunnel del gre1

On Debian GNU/Linux try the following:

GRE Tunnel Between Two Machines

This sets up a GRE tunnel between hosts 11.11.11.11 and 33.33.33.33.

  Physical interfaces:    [11.11.11.11]         [33.33.33.33]
  GRE tunnel:              22.22.22.11 <-------> 22.22.22.33

  ==== host 11.11.11.11 (GRE interface 22.22.22.11)
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
  ip link set gre1 down
  ip tunnel del gre1
  ip tunnel add gre1 mode gre remote 33.33.33.33 local 11.11.11.11 ttl 127
  ip addr add 22.22.22.11/24 peer 22.22.22.33/24 dev gre1
  ip link set gre1 up multicast on

  ==== host 33.33.33.33 (GRE interface 22.22.22.33)
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
  ip link set gre1 down
  ip tunnel del gre1
  ip tunnel add gre1 mode gre remote 11.11.11.11 local 33.33.33.33 ttl 127
  ip addr add 22.22.22.33/24 peer 22.22.22.11/24 dev gre1
  ip link set gre1 up multicast on

GRE Tunnels with Three Machines

STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!STOP!!!

IF YOU ADD MORE THAN TWO GRE TUNNELS IN A CHAIN, IT IS VERY EASY TO CREATE UNICAST ROUTING LOOPS, AND THIS MAY LEAD TO MULTICAST ROUTING LOOPS. MULTICAST ROUTING LOOP IS A DISASTER THAT MAY BRING YOUR WHOLE NETWORK DOWN. BEFORE ATTEMPTING THIS CONFIGURATION, MAKE SURE YOU UNDERSTAND VERY WELL WHAT YOU ARE DOING, AND WHAT MAY HAPPEN. IF YOU ARE READING THIS, THE CHANCES ARE THAT YOU DON'T KNOW, SO THINK AGAIN!!

THINK!!!THINK!!!THINK!!!THINK!!!THINK!!!THINK!!!THINK!!!THINK!!!THINK!!!

  Physical interfaces: [11.11.11.11]    [33.33.33.33]    [55.55.55.55]
  GRE tunnels:          22.22.22.11 <--> 22.22.22.33
                                         44.44.44.33 <--> 44.44.44.55
  
  ==== host 33.33.33.33 (GRE interfaces 22.22.22.33 and 44.44.44.33)
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
  ip tunnel add gre1 mode gre remote 11.11.11.11 local 33.33.33.33 ttl 127
  ip addr add 22.22.22.33/24 peer 22.22.22.11/24 dev gre1
  ip link set gre1 up multicast on
  ip tunnel add gre2 mode gre remote 55.55.55.55 local 33.33.33.33 ttl 127
  ip addr add 44.44.44.33/24 peer 44.44.44.55/24 dev gre2
  ip link set gre2 up multicast on

  ==== host 55.55.55.55 (GRE interface 44.44.44.55)
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
  ip tunnel add gre1 mode gre remote 33.33.33.33 local 55.55.55.55 ttl 127
  ip addr add 44.44.44.55/24 peer 44.44.44.33/24 dev gre1
  ip link set gre1 up multicast on
  route add -net 22.22.22.0 netmask 255.255.255.0 gw 44.44.44.33 gre1

  ==== host 11.11.11.11 (GRE interface 22.22.22.11)
  echo 1 > /proc/sys/net/ipv4/ip_forward
  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
  ip tunnel add gre1 mode gre remote 33.33.33.33 local 11.11.11.11 ttl 127
  ip addr add 22.22.22.11/24 peer 22.22.22.33/24 dev gre1
  ip link set gre1 up multicast on
  route add -net 44.44.44.0 netmask 255.255.255.0 gw 22.22.22.33 gre1

The pimd.conf FAQ

For a complete list of all available options, see pimd.conf and the man page.

  1. How to disable pimd being Cand-RP?

    Comment-out the rp-candidate and group-prefix lines in pimd.conf

  2. How to disable pimd being Cand-BSR?

    Comment-out the bsr-candidate line in pimd.conf

  3. How to prevent a prefix of multicast addresses being routed through my multicast router?

    If you want to scope, say, prefixes 238.0.0.0/8 and 239.0.0.0/8, add the following lines to pimd.conf:

     phyint eth1 scoped 238.0.0.0 masklen 8
 phyint eth1 scoped 239.0.0.0 masklen 8

  4. How to create a scope zone and stop multicast packets for some multicast prefix being propagated beyond the boundary of my network?

    Add scoping filters on your border routers for each prefix you want to scope. E.g.:

     phyint eth1 scoped 239.0.0.0 masklen 8
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