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Routing

  • IGMP Version 2

    IGMP Version 2 uses a message format 32 bits in size, with three fields. The first 8 bits are the type, the next 8 bits are the max response time, and the final 16 bits are a checksum. This message is encapsulated inside of an IP packet with a protocol number of 2. The message…

  • Internet Group Management Protocol (IGMP)

    IGMP, Internet Group Management Protocol, is a protocol that hosts/receivers use to join multicast groups and begin receive the groups multicast traffic. In order for Internet Group Management Protocol to work correctly, both the hosts and the router must support IGMP. When the host wishes to receive a multicast stream, it advertises to the router…

  • Multicast: Layer 2 Addresses

    On older network interface cards, the hardware would only traffic destined to it’s burned in MAC address or the broadcast MAC address. Multicast on Layer 2 was designed with this in mind. Every multicast group IP address is mapped to a special MAC address that will allow network interface cards to identify multicast packets to…

  • Multicast Addressing

    The Internet Assigned Number Authority (IANA) assigned IP Class D space for multicast addressing – 224.0.0.0/4 This includes the range 224.0.0.0 to 239.255.255.255 Address Range Description 224.0.0.0 – 224.0.0.255 Local Network Control 224.0.1.0 – 224.0.1.255 Internetwork Control 224.0.2.0 – 224.0.255.255 Ad-hoc 1 224.1.0.0 – 224.1.255.255 Reserved 224.2.0.0 – 224.2.255.255 SDP/SAP 224.3.0.0 – 224.4.255.255 Ad-hoc 2…

  • Multicast

    IP communication between hosts uses one of three transmission methods: unicast, broadcast, or multicast. If there is a group of five different hosts, and three wish to view an identical video stream, multicast would be the best transmission method to be used. Unicast would result in inefficiency by using triple the bandwidth that would be…

  • BGP Path Attributes: Lowest Neighbour Address

    The last deciding factor on choosing a best path is to select the path that comes from the lowest BGP neighbour address. Only iBGP applies here as eBGP would of been determined using the oldest received path earlier in the chain.

  • BGP Path Attributes: Minimum Cluster List Length

    With a tie on the Router ID, it falls to the minimum cluster list length to try break the deadlock. The step uses the cluster list to locate the path that has travelled the least number of iBGP advertisement hops. The cluster list is a non-transitive BGP attribute that is appended by a router reflector…

  • BGP Path Attributes: Router ID / RID

    With the oldest eBGP path ending in a tie, or into iBGP paths, the next step for the best path algorithm is to choose the best path from the session with the lowest Router ID of the advertising router. If it was a route reflector that advertised the route, then the originator ID is substituted…

  • BGP Path Attributes: Prefer the oldest eBGP Path

    If the lowest IGP metric ends in a tie, the oldest eBGP session is preferred simply for its stability.

  • BGP Path Attributes: Lowest IGP Metric

    If there is a tie on the eBGP over iBGP decison, lowest IGP metric is examined next. It is simply a comparison of metrics to the destination, the lowest metric to the next-hop destination is the preferred path.