Video: SD-WAN Security

After discussing the backend and CPE architecture in a typical SD-WAN solution in the SD-WAN Overview webinar, Pradosh Mohapatra mentioned a few SD-WAN security aspects, focusing on typical attack vectors and the usual mitigations.

Video: SD-WAN Security

After discussing the backend and CPE architecture in a typical SD-WAN solution in the SD-WAN Overview webinar, Pradosh Mohapatra mentioned a few SD-WAN security aspects, focusing on typical attack vectors and the usual mitigations.

Are LACP Fast Timers Any Good?

Got this question from a networking engineer attending the Building Next-Generation Data Center online course:

Has anyone an advice on LACP fast rate? When and why should you use it instead of normal LACP?

Apart from forming link aggregation groups, you can use LACP to detect link- and node failures (more details). However:

Are LACP Fast Timers Any Good?

Got this question from a networking engineer attending the Building Next-Generation Data Center online course:

Has anyone an advice on LACP fast rate? When and why should you use it instead of normal LACP?

Apart from forming link aggregation groups, you can use LACP to detect link- and node failures (more details). However:

Distributed Systems Resources

Distributed systems are complicated. Add networking to the mix, and you get traumatic challenges like the CAP theorem and Byzantine fault tolerance. Most of those challenges are unknown to engineers who have to suffer through the vendor marketing presentations, making it hard to determine whether the latest shiny gizmo works outside of PowerPoint.

I started collecting articles describing distributed-system gotchas years ago, wrote numerous blog posts on the topic in the heydays of the SDN Will Save the World lemming run, and organized them into the Distributed Systems Resources page.

Distributed Systems Resources

Distributed systems are complicated. Add networking to the mix, and you get traumatic challenges like the CAP theorem and Byzantine fault tolerance. Most of those challenges are unknown to engineers who have to suffer through the vendor marketing presentations, making it hard to determine whether the latest shiny gizmo works outside of PowerPoint.

I started collecting articles describing distributed-system gotchas years ago, wrote numerous blog posts on the topic in the heydays of the SDN Will Save the World lemming run, and organized them into the Distributed Systems Resources page.

EIGRP Third-Party Next Hops

EIGRP routing updates have always contained the next hop field (similar to BGP updates), which was unused until Cisco IOS release 12.3 when the no ip next-hop-self eigrp AS-number interface configuration command was implemented.

EIGRP does not set the next hop field by default. An EIGRP router receiving a routing update thus assumes that the next hop of the received routes is the sending router. This behavior usually works well, but prevents site-to-site shortcuts to be established in DMVPN networks, and results in suboptimal routing in some route redistribution scenarios.

EIGRP Third-Party Next Hops

EIGRP routing updates have always contained the next hop field (similar to BGP updates), which was unused until Cisco IOS release 12.3 when the no ip next-hop-self eigrp AS-number interface configuration command was implemented.

EIGRP does not set the next hop field by default. An EIGRP router receiving a routing update thus assumes that the next hop of the received routes is the sending router. This behavior usually works well, but prevents site-to-site shortcuts to be established in DMVPN networks, and results in suboptimal routing in some route redistribution scenarios.

Default EBGP Policy (RFC 8212)

One of the most common causes of Internet routing leaks is an undereducated end-customer configuring EBGP sessions with two (or more) upstream ISPs.

Without basic-level BGP knowledge or further guidance from the service providers, the customer network engineer¹ might start a BGP routing process and configure two EBGP sessions, similar to the following industry-standard CLI² configuration:

Default EBGP Policy (RFC 8212)

One of the most common causes of Internet routing leaks is an undereducated end-customer configuring EBGP sessions with two (or more) upstream ISPs.

Without basic-level BGP knowledge or further guidance from the service providers, the customer network engineer¹ might start a BGP routing process and configure two EBGP sessions, similar to the following industry-standard CLI² configuration:

Worth Reading: Internet WAN Edge Design

Brandon Hitzel published a detailed document describing various Internet WAN edge designs. Definitely worth reading and bookmarking.

Worth Reading: Internet WAN Edge Design

Brandon Hitzel published a detailed document describing various Internet WAN edge designs. Definitely worth reading and bookmarking.

Worth Reading: Unbounded TCP Memory Usage

Another phenomenal detective story published on Cloudflare blog: Unbounded memory usage by TCP for receive buffers, and how we fixed it.

TL&DR: Moving TCP window every time you acknowledge a segment doesn’t work well with scaled window sizes.

The interesting takeaways:

Worth Reading: Unbounded TCP Memory Usage

Another phenomenal detective story published on Cloudflare blog: Unbounded memory usage by TCP for receive buffers, and how we fixed it.

TL&DR: Moving TCP window every time you acknowledge a segment doesn’t work well with scaled window sizes.

The interesting takeaways:

Video: Link State Routing Protocol Basics

After introducing the routing protocols and explaining the basics of link-state routing it was time for implementation considerations including:

• Collecting local endpoint reachability information
• Finding neighbors and exchanging the collected information (hint: a link-state topology database is just a distributed key-value store)
• Running the SPF algorithm (including partial SPF details) and installing the results

Video: Link State Routing Protocol Basics

After introducing the routing protocols and explaining the basics of link-state routing it was time for implementation considerations including:

• Collecting local endpoint reachability information
• Finding neighbors and exchanging the collected information (hint: a link-state topology database is just a distributed key-value store)
• Running the SPF algorithm (including partial SPF details) and installing the results

Source IP Address in Multicast Packets

One of my readers sent me this (paraphrased) question:

What I have seen in my network are multicast packets with the IP source address set to 0.0.0.0 and source port set to 0. Is that considered acceptable? Could I use a multicast IP address as a source address?

TL&DR: **** NO!!!

It also seemed like a good question to test ChatGPT, and this time it did a pretty good job.

Source IP Address in Multicast Packets

One of my readers sent me this (paraphrased) question:

What I have seen in my network are multicast packets with the IP source address set to 0.0.0.0 and source port set to 0. Is that considered acceptable? Could I use a multicast IP address as a source address?

TL&DR: **** NO!!!

It also seemed like a good question to test ChatGPT, and this time it did a pretty good job.

NTP in a Nutshell

Years ago I’ve been involved in an interesting discussion focusing on NTP authentication and whether you can actually implement it reliably on Cisco IOS. What I got out of it (apart from a working example) was the feeling that NTP and it’s implementation in Cisco IOS was under-understood and under-documented, so I wrote an article about it. Of course the web version got lost in the mists of time but I keep my archives handy.

Last weekend I migrated that article to blog.ipSpace.net. I hope you’ll still find it useful; while it’s pretty old, the fundamentals haven’t changed in the meantime.

NTP in a Nutshell

Years ago I’ve been involved in an interesting discussion focusing on NTP authentication and whether you can actually implement it reliably on Cisco IOS. What I got out of it (apart from a working example) was the feeling that NTP and it’s implementation in Cisco IOS was under-understood and under-documented, so I wrote an article about it. Of course the web version got lost in the mists of time but I keep my archives handy.

Last weekend I migrated that article to blog.ipSpace.net. I hope you’ll still find it useful; while it’s pretty old, the fundamentals haven’t changed in the meantime.