Author Archive

Reserved MPLS labels

A table showing some of the more important reserved MPLS labels. I’ll add more on these labels in a later post.

Label Value
LDP
TDP

0
IPv4 Explicit Null
IPv4 Implicit Null

1
Router Alert
IPv4 Implicit Null

2
IPv6 Explicit Null
Router Alert

3
IPv4 Implicit Null
IPv6 Explicit Null

ISIS level-1, level-2 areas, ISIS redistribution and ISIS default route origination.

I’m going to cover following three things in this post.

Level-1, Level-1-2 and Level-2-only routers.  How to configure and what is the att bit
Investigate the default behavior of the various levels with respect to routing updates.  ie are level-2 prefixes by default advertised to level-1 routers.
Finally we will cover how to originate a default route within [...]

ISIS over Frame-Relay

Configuring ISIS over frame-relay requires an additional command due to the fact that ISIS packets do not use IP at layer 3 but rather use CLNS.
Consider the topology below.

Watch the video below or alternatively download it and watch it on your iPod .

The commands used in the configuration can be found below.
R1
!
frame-relay switching
!
interface Serial1/0
ip address [...]

ISIS wide metrics

Be default ISIS caps ISIS metrics greater than 63.
To address this limitation a new IS-IS TLV was defined to overcome the limited 6-bit metric of 63.  This TLV known as TLV Type 135 increased the per-link metric range from to ie the new TLV has 24-bits for the ISIS metric.
This new range can [...]

Prefix Lists

IP Prefix lists can be used with BGP to permit or deny specific prefixes from being advertised or learnt to or from a neighbor.
Consider the topology below.

We will carry out three exercises.

configure a prefix list to match 192.168.1.0/24
configure a prefix list to match 192.168.1.0/24, 192.168.1.0/25, 192.168.1.0/26.
configure a prefix list to match 192.168.1.0/25 and 192.168.1.0/26

Exercise 1
We [...]

ARF – Automatic Route Filtering

When designing an MPLS network you will have to decide whether to configure a full mesh of MP-iBGP sessions between your PEs as in diagram 1 below or whether to use a hub and spoke topology as in diagram 2 below.
Diagram 1 – BGP full mesh

Diagram 2 – BGP partial mesh

The most obvious benefit of [...]

New Cisco Certifications Logo

I came across this link recently.  It suggests that Cisco Certification Logos are changing.
Follow the link to see the new logos.

AFIs and SAFIs

BGP uses Open messages to negotiate BGP sessions.  These Open messages have optional parameters which allow additional capabilities to be negotiated during setup.
If you want to run anything other than IPv4 unicast then you will have to configure BGP to advertise its additional capabilities i.e. Multi-Protocol extensions (AFI/SAFI) during initial setup.
As an example you may [...]

BGP Route Aggregation

There are times when it is required to aggregate a set of prefixes.  There are a number of reasons why you would want to do this such as, your peering transit edge may not accept certain size prefixes, you may want to reduce the size of the routing table in some part of your network [...]

Source Based RTBH

Consider the topology below.

PC1 sends a syn flood attack using source IP 192.168.1.1 to PC2 destination address 172.16.1.1.
The network engineer at ZeeNet spots the attack and quickly logs onto the trigger router.  He adds a static route to the trigger router which states that the next hop for 192.168.1.1/32 is Null0.  This static route is [...]