In the world of internet networking, Autonomous System Numbers (ASNs) play a crucial role in routing data efficiently between different networks. ASNs are unique identifiers assigned to Autonomous Systems (AS)—large networks or groups of IP addresses that operate under a single organization, such as ISPs, cloud providers, or large enterprises. However, not all ASNs are […]
Yesterday I posted a tricky question to Twitter. If you have a working VPNv4 environment and create a VRF with only a Route Distinguisher (RD) but without Route Targets (RT), will the route be exported? The answer may surprise you! The configuration supplied in the question was similar to the one below: vrf definition QUIZ […]
BGP is a path vector protocol. This is similar to distance vector protocols such as RIP. Protocols like these, as opposed to link state protocols such as OSPF and ISIS, are not aware of any topology. They can only act on information received by peers. Information is not flooded in the same manner as IGPs […]
Valley-free routing is a concept that may not be well known but that is relevant to datacenter design. In this post, we’ll valley-free routing based on a leaf and spine topology. There are many posts about leaf and spine topology and the benefits. To summarize, some of the most prominent advantages are: Predictable number of […]
I’ve been in a lot of interesting discussions the last couple of days on what protocol to use for the underlay when building a VXLAN datacenter network. Do you use an IGP such as OSPF or ISIS or do you use BGP? A common argument for BGP is that running one protocol is less complex […]
In one of the Discords that I’m in there was a user with a complex network consisting of a mix of DMVPN, BGP over MPLS VPN circuits, and SD-WAN. For some prefixes, the path via the private MPLS is preferred, for others, the SD-WAN path. Now, if a prefix is available in two different protocols, […]
Introduction In the previous post I showed some of the options to interconnect two AS so that a customer can buy a VPN in two different locations from two different SPs. There is another technology called Carrier Supporting Carrier or Carrier of Carriers. This technology is used when a customer buys a circuit from an […]
Introduction Sometimes a customer needs a L3 VPN between two locations where the same SP is not present. This can be on a national or international basis. It would be possible to buy an Internet circuit and run an overlay such as DMVPN but what if the customer wants to buy a MPLS VPN circuit? […]
Introduction BGP Confederations are one of two tools a network designer has to work around the full mesh requirement of iBGP. BGP confederations are defined in RFC 5065 which obsoletes RFC 3065. This is how the RFC defines BGP confederations: This document describes an extension to BGP that may be used to create a confederation […]
In some publications it is mentioned that a link local next-hop can’t be used when redistributing routes into BGP because routers receiving the route will not know what to do with the next-hop. That is one of the reason why HSRPv2 got support for global IPv6 addresses. One such scenario is described in this link. […]
