Chapter : Multicasting 223
Router User Guide
n Modulo-N Hash —To select a next-hop from the list of N next-hops, the router performs a
modulo-N hash over the packet header fields that identify a flow.”
n Hash-Threshold—The router first selects a key by performing a hash over the packet header
fields that identify the flow. The N next-hops have been assigned unique regions in the hash
functions output space. By comparing the hash value against region boundaries the router can
determine which region the hash value belongs to and thus which next-hop to use.
n Highest Random Weight (HRW)—The router computes a key for each next-hop by
performing a hash over the packet header fields that identify the flow, as well as over the
address of the next-hop. The router then chooses the next-hop with the highest resulting key
value.
The Round-Robin and Random methods are disruptive by design (that is, if there is no change to the
set of next-hops, the path a flow takes changes every time). Modulo-N, Hash Threshold, and HRW
are not disruptive.
RFC 2991 recommends to use HRW method to select the next-hop for multicast packet forwarding.
or this reason,
Alcatel-only scenarios apply the HRW method as the default. This is similar to the
Cisco Systems IPv6 multicast multipath implementation.
Multipath Commands
The following table lists the multipath commands:
When multipath is disabled, Alcatel selects the nexthop address with lowest ip address. For equal
cost routes the nexthops are stored in the increasing (ascending) order of IP address. show ip
rpf command displays the selected path, based on the configured multipath method and the
nexthops of the best route to the IP address passed.
Generic Routing Encapsulation (GRE)
Generic Routing Encapsulation (GRE) handles the transportation of IP multicast traffic between two
sites that have only IP unicast connectivity. Using tunnels in a VPN environment is important
because IPSec encryption is limited to IP unicast frames. IPSec over GRE tunneling allows for the
encryption and the transportation of multiprotocol traffic across the VPN since both unicast and
multicast IP packets appear to the IPSec protocol as IP unicast frame after GRE tunneling. If all
connectivity must go through the home gateway router, tunnels also enable the use of private
network addressing across a service provider's backbone without the need for running the Network
Address Translation (NAT) feature.
The Alcatel implementation of the Generic Routing Encapsulation (GRE) tunneling protocol is
based on standards RFC1701 and RFC2784.
Enabling HRW method /configure/ip/multicast> multipath
Enabling Cisco method /configure/ip/multicast> multipath cisco
Disabling Multipath /configure/ip/multicast> no multipath
/configure/ip/multicast> no multipath cisco
Display RPF selection
Alcatel> show
ip rpf <addr>
<addr> - source or RP address
To Next Page
Loading...
Need help?
General
