FTOS Configuration Guide for the C-Series - Force10 Networks

Protocol Control Traffic Redirected Through MAC
Protocol control traffic in FTOS is redirected through the MAC address. In an InterVLAN scenario, certain
types of multicast traffic may hit the CPU in addition to normal Layer 2 flooding, since multiple Multicast
IP addresses and Layer 2 traffic both map to the same MAC address. For example, 224.0.0.5 is a well
known IP address for OSPF that maps to the multicast MAC address 01:00:5e:00:00:05. The Layer 2 FIB
alone can not differentiate multicast control traffic, such as OSPF or RIPv2, from certain multicast data
traffic. Since addresses such as 224.0.0.5, 225.0.0.5, 226.0.0.5, etc. all map to this same multicast MAC
address, the data traffic and OSPF traffic hit the same entry and are forwarded to the CPU. Therefore,
Force10 recommends to avoid using those multicast IP address that map to well-known MAC addresses
for data transmission.
As the upper five bits of an IP Multicast address are dropped in the translation, 32 different multicast group
IDs all map to the same Ethernet address. For example, when the user uses IP address 225.0.0.5 that maps
to the same multicast MAC address 01:00:5e:00:00:05, the traffic is treated as an OSPF multicast entry and
is also sent to the CPU.
Here are well known MAC addresses that are used in the system:
• OSPF 01:00:5e:00:00:05
• OSPF 01:00:5e:00:00:06
• RIP 01:00:5e:00:00:09
• NTP 01:00:5e:00:01:01
• VRRP 01:00:5e:00:00:12
• PIMSM 01:00:5e:00:00:0d
Multicast Traceroute
Multicast Traceroute is supported only on platforms e
MTRACE is an IGMP protocol based on the multicast traceroute facility which is implemented as per the
IETF draft draft-fenner-traceroute-ipm. FTOS supports mtrace client and mtrace transmit functionality.
Mtrace Client
When acting as an mtrace client, FTOS transmits mtrace queries, and receives, parses, and prints out the
details in the recieved response packets.
Mtrace Transit
When acting as an mtrace transit or intermediate router, FTOS returns the response to mtrace queries.
Upon receiving an mtrace request, FTOS computes the RPF neighbor for the source, fills in the request,
and forwards the request to the RPF neighbor. While computing the RPF neighbor, static mroutes and
mBGP routes are preferred over unicast routes.
636 Multicast Features