This MIB contains information about NextHop Groups (NHG).

General L3 routing creates routing table entries, each of
which are associated with a nexthop. If multiple paths
exist for a specific route, the route points to a set of
nexthops (commonly referred as ECMP or Equal Cost
MultiPath).

Arista devices support a feature which allows customers to
manually create a nexthop list, and use this list to
route packets to the specified set of nexthop
addresses. Customers can associate a tunnel type (GRE,
for example) with the nexthop group, allowing relevant
packets to be tunneled as well. The packet forwarding or
routing decision happens in hardware. 

Nexthop group feature gives customers full control of how
a route should be forwarded (tunneled or otherwise). The
number of entries in the nexthop group is also determined
by the user, and directly translates to the number of
nexthop entries in the hardware for the specified route.

Let's provide an example, looking at EOS CLI example.

nexthop-group foo type ip-in-ip
  ttl 64 
  entry 0 tunnel-destination 10.1.1.1 
  entry 1 tunnel-destination 20.1.1.1 
!
ip route 30.1.1.0/24 Nexthop-Group foo

In the above configuration, any packet destined to
30.1.1.0/24 will be forwarded by the nexthop group
'foo'. Each entry inside the nexthop group specifies a
particular nexthop ('tunnel destination') chosen by the
customer. In this example, packets can be forwarded via
either of the nexthop (traffic split equally between the 2
entries).

This MIB module provides information relevant to the
nexthop group feature, specifically the status of various
nexthop groups configured, and traffic statistics.