Dynamic Routing - GE MDS ORBIT MCR Technical Manual

3.8.21

Dynamic Routing

Understanding
Dynamic routing consists of routers building and maintaining routing tables automatically through an
ongoing communication between them. This communication is facilitated by a routing protocol, which
consists of a series of periodic or on-demand messages containing routing information that is exchanged
between the routers.
The unit supports following routing protocols to enable dynamic routing:

Routing Information protocol (RIP)- The unit support RIPv2 (RFC 1723, RFC4822)

Open Shortest Path First (OSPF) – The unit supports OSPFv2 (RFC 2328)

Border Gateway Protocol (BGP) – The unit support BGPv4 (RFC 4271).
Following reference can be consulted for a technical overview of RIP:
http://docwiki.cisco.com/wiki/Routing_Information_Protocol
Following reference can be consulted for a technical overview of OSPF:
http://docwiki.cisco.com/wiki/Open_Shortest_Path_First
Following reference can be consulted for a technical overview of BGP:
http://docwiki.cisco.com/wiki/Border_Gateway_Protocol
The user can control the routes that are imported into the routing table from the routing protocol and those
that are exported into the routing protocol from the routing table by using route filters.
The import route filter controls the routes that are imported into the routing table by the routing protocol.
By default, the routing protocol allows all routes received from the peer router to be imported into the
routing table. That is, if no import filter is configured, default action is ACCEPT.
The export route filter controls the routes that are exported into the routing protocol from the routing
table. By default, the routing protocol prevents export of any routes from the local routing table to the
peer router. That is, if no export filter is configured, default action is NONE.
A route filter consists of one or more rules sorted by a numeric identifier. Each rule in route filter consists
of 'match' and 'actions' configuration. The parameters in the match are compared against the route being
imported (if this route filter is used as import filter) or exported (if this route filter is used as export filter)
into/from the routing table. If the route matches, the action (ACCEPT OR REJECT) specified in the
actions configuration is applied.
When routing protocol receives a route from the peer router it checks whether the route is allowed by the
import filter by comparing it against one or more rules configured in the filter (in order of their
configuration). If any rule matches, the corresponding action (ACCEPT or REJECT) is applied. Similarly,
for each route in the routing table, the routing protocol checks whether it is allowed by the export filter
before exporting it to the peer routers. In addition, some general attributes of the route like NEXT-HOP or
routing protocol specific attributes like BGP AS-PATH, LOCAl-PREF etc can be modified when
exporting routes using 'set'.
Use Cases
The figure below describes one of the use cases for dynamic routing on the unit. In this case, dynamic a
routing protocol is used to exchange locally connected LAN route with a router in the back-office (and
vice versa) over the Cellular WAN interface. Both OSPF and RIP exchange routing updates with peers
342 MDS Orbit MCR/ECR Technical Manual MDS 05-6632A01, Rev. F