Category: Routing

How does BGP select it’s path

BGP can be a complex and almost mystical protocol. For those of you who are trying to determine how BGP selects which route here is your guide. Before we get into it a couple of things to keep in mind. First, BGP is not a multipath routing protocol. This is different than what you may be used to with OSPF. BGP goes to great lengths to encure only one route is used. Secondly, there are […]

Ethernet MTU & Overhead

One of the most common questions is how much overhead do I need to account for on my transport network? I have put together a quick list to help when you are calculating your overhead. -GRE (IP Protocol 47) (RFC 2784): 24 bytes (20 byte IPv4 header, 4 byte GRE header) -6in4 encapsulation (IP Protocol 41, RFC 4213): 20 bytes -4in6 encapsulation (e.g. DS-Lite RFC 6333): 40 bytes Addition IPv4 header:20 bytes -IPsec encryption: 73 […]

OSPF Network Types

Point-to-multipoint is treated as a collection of point-to-point links and thus no DR/BDR is required. Point-to-Point is a single link and no election is needed. Broadcast: OSPF routers on broadcast networks will elect a DR and a BDR (since it is multiaccess) – OSPF packets are multicast. NBMA: Routers will elect DR and BDR (since it is multiaccess), but since it is a non-broadcast, routers will have to communicate via unicast rather than multicast.