Enterprise Routing Protocols: VRRP, STP, RIP, OSPF, and BGP

With the recent 4.1 and 4.2 firmware releases, we have bulked up our arsenal of advanced routing protocols, adding all of the following protocols to Cradlepoint COR and to the MBR1400 and ARC MBR1400:

  • VRRP – Virtual Router Redundancy Protocol
  • STP – Spanning Tree Protocol
  • Dynamic Routing Protocols:
    • RIP – Routing Information Protocol
    • OSPF – Open Shortest Path First 
    • BGP – Border Gateway Protocol
(Note that these protocols require hardware version 2.0 of the MBR1400.)
 

VRRP – Virtual Router Redundancy Protocol

VRRP allows you to associate multiple routers with one LAN so that if the primary physical router fails, a secondary router will switch to take the duties of the primary router. This adds another important layer to a business continuity system. Previously Cradlepoint routers were used as failover solutions behind other routers, but only for if the WAN failed, rather than the router itself. Now with VRRP, if the primary router fails, the network stays up.

vrrp_diagram

 
One router is set as the "master," and a second router is set as "backup". If the master router fails, the backup becomes the master with the same "virtual" IP address.
 

STP – Spanning Tree Protocol

STP allows a network design to prevent bridge loops while still including redundant paths. As the name suggests, Spanning Tree Protocol creates a "spanning tree," a graph theory term for a set of connected edges that hits all the vertices in a connected graph, but without any loops.
![spanning][spanning]
By eliminating loops, STP prevents unwanted broadcast radiation. STP still allows for redundancy by automatically finding an alternate path if a link fails.
 

Dynamic Routing Protocols: RIP, OSPF, and BGP

The larger the network, the more complex. Additional layers mean that there are additional hops for packets to go from one end of the network to the other, but by default a router only knows its immediate neighbors. A packet can't go across multiple layers of a network without the routers knowing the broader topology. Previously with Cradlepoint routers, this topology had to be inputted manually with "static routes." Now with RIP, OSPF, and BGP, Cradlepoint routers can learn the topology dynamically.
 
All of these routing protocols specify how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a network. Routing algorithms choose the route. Each router has a prior knowledge only of networks attached to it directly, but a routing protocol shares this information with immediate neighbors and then throughout the network. This way, routers learn the network topology.
 

RIP – Routing Information Protocol (versions 1 and 2)

RIP is used to synchronize the routing table of all the routers on a network. RIP is an older, more established protocol, but it has significant limitations, especially for larger networks. It is relatively simple in that it measures the distance of a route by hop count, which doesn't factor in traffic costs. To prevent infinite loops, the hop count is limited to 15, which can be a limitation if the network is large enough.
 
RIP causes routers to broadcast their entire current routing database periodically (30 seconds by default). This system is straightforward, but it causes slow convergence.
 

OSPF – Open Shortest Path First (version 2)

OSPF is used more than RIP in larger scale networks because it has a more efficient system for communication between routers and because it scales better to larger networks. Only changes to the routing table are sent to all the other routers in the network, as opposed to sending the entire routing table at a regular interval (which is how RIP functions).
 
OSPF is a link-state protocol – each router on the network shares its "link-state," which is the basic information of that router and its immediate connections. The OSPF protocol pieces together the information from all the link-states throughout the network to create a complete mapping. It then uses the Dijkstra algorithm to calculate the shortest path between any two points.
 

BGP – Border Gateway Protocol (version 4)

BGP is widely used across the Internet, but usually externally rather than internally. Internal use of BGP is typically only for very large networks. For example, it might be used as a connection between multiple networks that are already using OSPF, when the whole network is too large for OSPF by itself. BGP is unique in that it uses TCP as its transport protocol. It is commonly used as the protocol between Internet service providers. It includes cost metrics for each path so that packets take the most efficient route.