Author Archives: routingcraft

Explicit Null in Segment Routing

MPLS is such a user-friendly technology it needs a special label that does nothing.

Why explicit null

Normally, the penultimate router in the LSP removes (pops) the top transport label, so that the egress LSR will deal either with the …

Anycast in Segment Routing

MPLS or Anycast Routing – for a long time, you had to choose one. Segment Routing allows you to have both.


It’s hard to overstate how important anycast routing is. DNS root servers and CDN rely on it to …

ARP problems in EVPN

In any L2 overlay network, ARP handling will always remain a big pain for network operators.

This post explains why you should always set ARP timeout to less than 5 minutes in L3 EVPN, and always be cautious of potential …

Equal Routes

In highload cloud networks there is so much traffic that even 100G/400G port speeds do not suffice, so sharing the load over multiple links is the only feasible solution.


ECMP stands for Equal Cost Multi-Path – when a route …

Segregated Routing

For any network that provides routing services to customers it is important to segregate them in different virtual topologies that don’t interfere with each other.

Network Virtualization

This post is not about NFV, but it is important to understand …

Close to the Edge

PE-CE routing in MPLS L3VPN is an important topic which confuses a lot of people. Thanks to EVPN, it is now used not only in ISP but also DC networks.

Fundamentals of PE-CE routing

Usually either static routing or eBGP …

On Duplicates

Packet duplication wastes bandwidth and can lead to significant network performance degradation or even outages.

In multicast routing, packets are replicated by the network, so there is always a fundamental risk of duplicate traffic. Special safeguards exist to avoid …

Topology Dependent LFA

Fast convergence after failures has always been an important part of ISP network design.


When a failure is detected, it takes a while until the routing protocol propagates new information throughout the network and all routers update their FIB. …

Barbaric Balancing

Recently I stumbled upon the IETF draft about PIM Designated Router Load Balancing (DRLB) and it reminded me of something absolutely barbaric.


In L3 multicast, load balancing is simple. If the RPF route is ECMP, the router can choose …

Seamless Suffering

This story is about the importance of remembering networking fundamentals when dealing with advanced routing topics.

Overview of Seamless MPLS

Seamless MPLS is a really neat design for large ISP networks. The idea is to overcome the scalability limitations of …