BGP AS Numbers for a Private MPLS/VPN Backbone

One of my readers was building a private MPLS/VPN backbone and wondered whether they should use their public AS number or a private AS number for the backbone. Usually, it doesn’t matter; the deciding point was the way they want to connect to the public Internet:

We also plan to peer with multiple external ISPs to advertise our public IP space not directly from our PE routers but from dedicated Internet Routers, adding a firewall between our PEs and external Internet routers.

They could either run BGP between the PE routers, firewall, and WAN routers (see BGP as High-Availability Protocol for more details) or run BGP across a bump-in-the-wire firewall:

BGP AS Numbers for a Private MPLS/VPN Backbone

One of my readers was building a private MPLS/VPN backbone and wondered whether they should use their public AS number or a private AS number for the backbone. Usually, it doesn’t matter; the deciding point was the way they want to connect to the public Internet:

We also plan to peer with multiple external ISPs to advertise our public IP space not directly from our PE routers but from dedicated Internet Routers, adding a firewall between our PEs and external Internet routers.

They could either run BGP between the PE routers, firewall, and WAN routers (see BGP as High-Availability Protocol for more details) or run BGP across a bump-in-the-wire firewall:

OSPF Summarization and Split Areas

In the Do We Still Need OSPF Areas and Summarization? I wrote this somewhat cryptic remark:

The routers advertising a summarized prefix should be connected by a path going exclusively through the part of the network with more specific prefixes. GRE tunnel also satisfies that criteria; the proof is left as an exercise for the reader.

One of my readers asked for a lengthier explanation, so here we go. Imagine a network with two areas doing inter-area summarization on /24 boundary:

OSPF Summarization and Split Areas

In the Do We Still Need OSPF Areas and Summarization? I wrote this somewhat cryptic remark:

The routers advertising a summarized prefix should be connected by a path going exclusively through the part of the network with more specific prefixes. GRE tunnel also satisfies that criteria; the proof is left as an exercise for the reader.

One of my readers asked for a lengthier explanation, so here we go. Imagine a network with two areas doing inter-area summarization on /24 boundary:

Cyber Crane Mesh Topology Built with netlab

Milan Zapletal submitted the source code for a huge lab topology they built with netlab. It has almost 50 routers and over 50 Linux nodes to emulate end-users and servers.

They used netlab to configure VLANs, VRFs, IS-IS, OSPF, EIGRP, BGP, MPLS, VXLAN, and EVPN. Imagine how long it would take to configure all that by hand using a more traditional labbing tool.

Cyber Crane Mesh Topology Built with netlab

Milan Zapletal submitted the source code for a huge lab topology they built with netlab. It has almost 50 routers and over 50 Linux nodes to emulate end-users and servers.

They used netlab to configure VLANs, VRFs, IS-IS, OSPF, EIGRP, BGP, MPLS, VXLAN, and EVPN. Imagine how long it would take to configure all that by hand using a more traditional labbing tool.

Worth Reading: Talent Gap in IT

If you need a good rant about Thought Leaders, Talent Gap, and Certification-Based-Hiring, look no further than I see a different gap from here!. Here’s a choice tidbit:

Every single job description that requires some sort of certification must be treated with suspicion. Demanding a certification usually means that you don’t know what you want, and you’re just outsourcing your thinking to someone else.

Have fun!

Worth Reading: Talent Gap in IT

If you need a good rant about Thought Leaders, Talent Gap, and Certification-Based-Hiring, look no further than I see a different gap from here!. Here’s a choice tidbit:

Every single job description that requires some sort of certification must be treated with suspicion. Demanding a certification usually means that you don’t know what you want, and you’re just outsourcing your thinking to someone else.

Have fun!

Worth Exploring: PCAP Analysis with Generative AI

John Capobianco published the source code of his Packet Buddy application on GitHub. It’s a Python UI that takes a PCAP file, converts it to JSON, and includes that JSON as part of the ChatGPT chat, allowing you to discuss the captured packets with ChatGPT.

His idea is one of the best uses of generative AI in networking I’ve seen so far, as long as you remember that you’re dealing with an overconfident intern who has no problem making up an answer just to sound smart. Have fun!

Finally, if you don’t want to use ChatGPT (I wouldn’t blame you) or send captured data into The Cloud, someone already adapted his idea to use local LLMs.

Worth Exploring: PCAP Analysis with Generative AI

John Capobianco published the source code of his Packet Buddy application on GitHub. It’s a Python UI that takes a PCAP file, converts it to JSON, and includes that JSON as part of the ChatGPT chat, allowing you to discuss the captured packets with ChatGPT.

His idea is one of the best uses of generative AI in networking I’ve seen so far, as long as you remember that you’re dealing with an overconfident intern who has no problem making up an answer just to sound smart. Have fun!

Finally, if you don’t want to use ChatGPT (I wouldn’t blame you) or send captured data into The Cloud, someone already adapted his idea to use local LLMs.

DMVPN Videos Are Free to Download

It looks like DMVPN is still kicking; every other blue moon, I get a “Thank you” note from someone figuring out the DMVPN details from my first DMVPN webinar, so I decided to make those videos public. You can watch any video from the DMVPN Technology and Configuration without registration.

A tangential note in case you’re wondering how “easy” it is to refurbish old stuff:

• The webinar was recorded as a WebEx ARF recording.
• The WebEx MP4 exporter I used when trying to generate videos from my old ARF files was broken and couldn’t produce usable videos after a long silence (I muted the microphone during a coffee break). I gave up at that time
• A few weeks ago, I decided to replay the recording and create videos from the screen capture.
• Finally, it took my audio editor quite a while to make the sound recorded with 8-bit 8 kHz codec (thank you, WebEx) sound better than Apollo 11 communications with Houston.

BGP Labs: Limit the Number of Accepted BGP Prefixes

Here’s an easy way to stop fat-finger incidents in which an end-user autonomous system redistributes IGP into BGP or advertises the whole DFZ routing table from affecting the entire Internet: limit the number of BGP prefixes your routers accept from your customers. You can practice this nifty feature in the next BGP lab exercise.

BGP Labs: Limit the Number of Accepted BGP Prefixes

Here’s an easy way to stop fat-finger incidents in which an end-user autonomous system redistributes IGP into BGP or advertises the whole DFZ routing table from affecting the entire Internet: limit the number of BGP prefixes your routers accept from your customers. You can practice this nifty feature in the next BGP lab exercise.

Multiline Expressions in Ansible Playbooks

Another week, another Ansible quirk 🤷‍♂️ Imagine you have a long Jinja2 expression, and you want to wrap it into multiple lines to improve readability. Using multiline YAML format seems to be the ideal choice:

---
- name: Test playbook
  hosts: localhost
  tasks:
  - set_fact:
      a: >
        {{ 123 == 345 or
           123 > 345 }}

It works every time 50% of the time (this time depending on your Ansible version).

Multiline Expressions in Ansible Playbooks

Another week, another Ansible quirk 🤷‍♂️ Imagine you have a long Jinja2 expression, and you want to wrap it into multiple lines to improve readability. Using multiline YAML format seems to be the ideal choice:

---
- name: Test playbook
  hosts: localhost
  tasks:
  - set_fact:
      a: >
        {{ 123 == 345 or
           123 > 345 }}

It works every time 50% of the time (this time depending on your Ansible version).

Rant: Multi-Vendor EVPN Fabrics

Daniel Dib tweeted about an old comment of mine a few days ago, adding¹:

Not surprisingly, that was bound to upset a few people, and Roman Dodin quickly pointed out the EVPN interoperability tests:

Rant: Multi-Vendor EVPN Fabrics

Daniel Dib tweeted about an old comment of mine a few days ago, adding¹:

Not surprisingly, that was bound to upset a few people, and Roman Dodin quickly pointed out the EVPN interoperability tests:

netlab 1.8.0: Control-Plane Daemons, BIRD, dnsmasq

I wanted to include open-source networking-related software into netlab topologies since (at least) the days I was writing the DHCP relaying saga. It turned out to be a bit more complex than I anticipated (more about that in another blog post), but I hope you’ll find it useful. netlab release 1.8.0 includes dnsmasq running as a DHCP server and BIRD running OSPF and BGP. ExaBGP and GoBGP are already on the wish list; if you have any other ideas, please start a GitHub discussion.

I had a hard time finding reasonable container images for BIRD; the BIRD team does not publish them, and everything else I found looked either abandoned or a hobby project. The solution turned out to be exceedingly simple: you cannot run the containers without Docker anyway, which means the docker build command is just a few keystrokes away. I added Dockerfiles needed to build those containers to the netlab source code and implemented the netlab clab build command as a thin wrapper around docker build. It takes just a few seconds (plus the time it takes to download the Ubuntu container image) to build the containers you need.

netlab 1.8.0: Control-Plane Daemons, BIRD, dnsmasq

I wanted to include open-source networking-related software into netlab topologies since (at least) the days I was writing the DHCP relaying saga. It turned out to be a bit more complex than I anticipated (more about that in another blog post), but I hope you’ll find it useful. netlab release 1.8.0 includes dnsmasq running as a DHCP server and BIRD running OSPF and BGP. ExaBGP and GoBGP are already on the wish list; if you have any other ideas, please start a GitHub discussion.

I had a hard time finding reasonable container images for BIRD; the BIRD team does not publish them, and everything else I found looked either abandoned or a hobby project. The solution turned out to be exceedingly simple: you cannot run the containers without Docker anyway, which means the docker build command is just a few keystrokes away. I added Dockerfiles needed to build those containers to the netlab source code and implemented the netlab clab build command as a thin wrapper around docker build. It takes just a few seconds (plus the time it takes to download the Ubuntu container image) to build the containers you need.

Worth Reading: Unbloating the Buffers

In case you’ve heard about bufferbloat but don’t know what it is: Dan Groshev wrote a nice bufferbloat for dummies blog post on the APNIC blog.