Worth Reading: Use of HTTPS DNS Resource Records

Around 30 years after we got the first website, the powers that be realized it might make sense to put this is how you access a web server information (including its IPv4 and IPv6 address, and HTTP(S) support information) directly into DNS, using HTTPS Resource Records. It took us long enough 🤷‍♂️

Worth Reading: Use of HTTPS DNS Resource Records

Around 30 years after we got the first website, the powers that be realized it might make sense to put this is how you access a web server information (including its IPv4 and IPv6 address, and HTTP(S) support information) directly into DNS, using HTTPS Resource Records. It took us long enough 🤷‍♂️

30 Days Left to Buy ipSpace.net Subscription

When I announced the lifetime ipSpace.net subscription in early September, I also mentioned that you won’t be able to purchase any ipSpace.net subscription after December 31st, 2023.

As of today, you have 30 days left to decide, and don’t wait till the last minute – I plan to turn off the purchasing process sometime during the business hours of December 31st as I hope to have more interesting things to do in the evening.

The BGP Multi-Exit Discriminator (MED) Saga

Martijn Van Overbeek left this comment on my LinkedIn post announcing the BGP MED lab:

It might be fixed, but I can recall in the past that there was a lot of quirkiness in multi-vendor environments, especially in how different vendors use it and deal with the setting when the attribute does exist or does not have to exist.

TL&DR: He’s right. It has been fixed (mostly), but the nerd knobs never went away.

In case you’re wondering about the root cause, it was the vagueness of RFC 1771. Now for the full story ;)

The BGP Multi-Exit Discriminator (MED) Saga

Martijn Van Overbeek left this comment on my LinkedIn post announcing the BGP MED lab:

It might be fixed, but I can recall in the past that there was a lot of quirkiness in multi-vendor environments, especially in how different vendors use it and deal with the setting when the attribute does exist or does not have to exist.

TL&DR: He’s right. It has been fixed (mostly), but the nerd knobs never went away.

In case you’re wondering about the root cause, it was the vagueness of RFC 1771. Now for the full story ;)

BGP Labs: Set BGP Communities on Outgoing Updates

It’s hard to influence the behavior of someone with strong opinions (just ask any parent with a screaming toddler), and trying to persuade an upstream ISP not to send the traffic over a backup link is no exception – sometimes even AS path prepending is not a strong enough argument.

An easy solution to this problem was proposed in 1990s – what if we could attach some extra attributes (called communities just to confuse everyone) to BGP updates and use them to tell adjacent autonomous systems to lower their BGP local preference? You can practice doing that in the Attach BGP Communities to Outgoing BGP Updates lab exercise.

BGP Labs: Set BGP Communities on Outgoing Updates

It’s hard to influence the behavior of someone with strong opinions (just ask any parent with a screaming toddler), and trying to persuade an upstream ISP not to send the traffic over a backup link is no exception – sometimes even AS path prepending is not a strong enough argument.

An easy solution to this problem was proposed in 1990s – what if we could attach some extra attributes (called communities just to confuse everyone) to BGP updates and use them to tell adjacent autonomous systems to lower their BGP local preference? You can practice doing that in the Attach BGP Communities to Outgoing BGP Updates lab exercise.

Can a Router Use the Default Route to Reach BGP Next Hops?

TL&DR: Yes.

Starting with RFC 4271, Route Resolvability Condition:

• A route without an outgoing interface is resolvable if its next hop is resolvable without recursively using the same route.
• A route with an outgoing interface is always considered resolvable.
• BGP routes can be resolved through routes with just a next hop or an outgoing interface.

Can a Router Use the Default Route to Reach BGP Next Hops?

TL&DR: Yes.

Starting with RFC 4271, Route Resolvability Condition:

• A route without an outgoing interface is resolvable if its next hop is resolvable without recursively using the same route.
• A route with an outgoing interface is always considered resolvable.
• BGP routes can be resolved through routes with just a next hop or an outgoing interface.

Worth Reading: Network Automation with GitHub Actions

George Davitiani put together a lovely proof-of-concept using GitHub actions to deploy modified configurations to network devices. Even better, he documented the whole setup, and the way to reproduce it. I’m positive you’ll find a few ideas browsing through what he did.

Worth Reading: Network Automation with GitHub Actions

George Davitiani put together a lovely proof-of-concept using GitHub actions to deploy modified configurations to network devices. Even better, he documented the whole setup, and the way to reproduce it. I’m positive you’ll find a few ideas browsing through what he did.

Worth Reading: Going CCNP Emeritus

Daniel Teycheney decided not to renew his CCNP status and used this opportunity to publish his thoughts on IT certifications. Not surprisingly, I agree with most of the things he said, but I never put it in writing so succinctly.

Red Pill Warning: Reading his blog post might damage your rosy view of the networking industry. You’ve been warned ;)

Worth Reading: Going CCNP Emeritus

Daniel Teycheney decided not to renew his CCNP status and used this opportunity to publish his thoughts on IT certifications. Not surprisingly, I agree with most of the things he said, but I never put it in writing so succinctly.

Red Pill Warning: Reading his blog post might damage your rosy view of the networking industry. You’ve been warned ;)

Video: Language Models in AI/ML Landscape

In September 2023, Javier Antich extended the AI/ML in Networking webinar with a new section describing large language models (LLMs), starting with how do the LLMs fit into the AI/ML landscape?

Video: Language Models in AI/ML Landscape

In September 2023, Javier Antich extended the AI/ML in Networking webinar with a new section describing large language models (LLMs), starting with how do the LLMs fit into the AI/ML landscape?

BGP Labs: AS-Path Prepending

In the previous lab, you learned how to use BGP Multi-Exit Discriminator (MED) to influence incoming traffic flow. Unfortunately, MED works only with parallel links to the same network. In a typical Redundant Internet Connectivity scenario, you want to have links to two ISPs, so you need a bigger hammer: AS Path Prepending.

BGP Labs: AS-Path Prepending

In the previous lab, you learned how to use BGP Multi-Exit Discriminator (MED) to influence incoming traffic flow. Unfortunately, MED works only with parallel links to the same network. In a typical Redundant Internet Connectivity scenario, you want to have links to two ISPs, so you need a bigger hammer: AS Path Prepending.

Why Do We Need BGP Identifiers?

A friend of mine sent me an interesting question along these lines:

We all know that in OSPF, the router ID is any 32-bit number, not necessarily an IP address of an interface. The only requirement is that it must be unique throughout the OSPF domain. However, I’ve always wondered what the role of BGP router ID is. RFC 4271 says it should be set to an IP address assigned to that BGP speaker, but where do we use it?

Also, he observed somewhat confusing behavior in the wild:

Take two routers and configure the same BGP identifier on both. Cisco IOS will not establish a session, while IOS XR and Junos will.

I decided to take the challenge and dug deep into the bowels of RFC 4271 and RFC 6286. Here’s what I brought back from that rabbit hole:

Why Do We Need BGP Identifiers?

A friend of mine sent me an interesting question along these lines:

We all know that in OSPF, the router ID is any 32-bit number, not necessarily an IP address of an interface. The only requirement is that it must be unique throughout the OSPF domain. However, I’ve always wondered what the role of BGP router ID is. RFC 4271 says it should be set to an IP address assigned to that BGP speaker, but where do we use it?

Also, he observed somewhat confusing behavior in the wild:

Take two routers and configure the same BGP identifier on both. Cisco IOS will not establish a session, while IOS XR and Junos will.

I decided to take the challenge and dug deep into the bowels of RFC 4271 and RFC 6286. Here’s what I brought back from that rabbit hole:

Is BGP TTL Security Any Good?

After checking what routers do when they receive a TCP SYN packet from an unknown source, I couldn’t resist checking how they cope with TCP SYN packets with too-low TTL when using TTL security, formally known as The Generalized TTL Security Mechanism (GTSM) defined in RFC 5082.

TL&DR: Not bad: most devices I managed to test did a decent job.