| .. _arpentries: |
| |
| ARP Entries |
| ^^^^^^^^^^^ |
| |
| .. figure:: /_images/fib20fig1.png |
| |
| Figure 1: ARP data model |
| |
| Figure 1 shows the data model for an ARP entry. An ARP entry contains the mapping |
| between a peer, identified by an IPv4 address, and its MAC address on a given |
| interface. The VRF the interface is bound to, is not part of the data. VRFs are |
| an ingress function not egress. The ARP entry describes how to send traffic to a |
| peer, which is an egress function. |
| |
| The *arp_entry_t* represents the control-plane addition of the ARP entry. The |
| *ip_adjacency_t* contains the data derived from the *arp_entry_t* that is need to |
| forward packets to the peer. The additional data in the adjacency are the *rewrite* |
| and the *link_type*. The *link_type* is a description of the protocol of the packets |
| that will be forwarded with this adjacency; this can be IPv4 or MPLS. The *link_type* |
| maps directly to the ether-type in an Ethernet header, or the protocol filed in a |
| GRE header. The rewrite is a byte string representation of the header that will be |
| prepended to the packet when it is sent to that peer. For Ethernet interfaces this |
| would be the src,dst MAC and the ether-type. For LISP tunnels, the IP src,dst pair |
| and the LISP header. |
| |
| The *arp_entry_t* will install a *link_type=IPv4* when the entry is created and a |
| link_type=MPLS when the interface is MPLS enabled. Interfaces must be explicitly |
| MPLS enabled for security reasons. |
| |
| So that adjacencies can be shared between route, adjacencies are stored in a single |
| data-base, the key for which is {interface, next-hop, link-type}. |