BGP Optimal Route Reflection 101

Almost a decade ago I described a scenario in which a perfectly valid IBGP topology could result in a permanent routing loop. While one wouldn’t expect to see such a scenario in a well designed network, it’s been known for ages¹ that using BGP route reflectors could result in suboptimal forwarding.

Here’s a simple description of how that could happen:

BGP Optimal Route Reflection 101

Almost a decade ago I described a scenario in which a perfectly valid IBGP topology could result in a permanent routing loop. While one wouldn’t expect to see such a scenario in a well designed network, it’s been known for ages¹ that using BGP route reflectors could result in suboptimal forwarding.

Here’s a simple description of how that could happen:

Why Does DHCPv6 Matter?

In case you missed it, there’s a new season of Lack of DHCPv6 on Android soap opera on v6ops mailing list. Before going into the juicy details, I wanted to look at the big picture: why would anyone care about lack of DHCPv6 on Android?

The requirements for DHCPv6-based address allocation come primarily from enterprise environments facing legal/compliance/other layer 8-10 reasons to implement policy (are you allowed to use the network), control (we want to decide who uses the network) and attribution (if something bad happens, we want to know who did it).

Why Does DHCPv6 Matter?

In case you missed it, there’s a new season of Lack of DHCPv6 on Android soap opera on v6ops mailing list. Before going into the juicy details, I wanted to look at the big picture: why would anyone care about lack of DHCPv6 on Android?

The requirements for DHCPv6-based address allocation come primarily from enterprise environments facing legal/compliance/other layer 8-10 reasons to implement policy (are you allowed to use the network), control (we want to decide who uses the network) and attribution (if something bad happens, we want to know who did it).

Graceful Restart and Routing Protocol Convergence

I’m always amazed when I encounter networking engineers who want to have a fast-converging network using Non-Stop Forwarding (which implies Graceful Restart). It’s even worse than asking for smooth-running heptagonal wheels.

As we discussed in the Fast Failover series, any decent router uses a variety of mechanisms to detect adjacent device failure:

• Physical link failure;
• Routing protocol timeouts;
• Next-hop liveliness checks (BFD, CFM…)

Graceful Restart and Routing Protocol Convergence

I’m always amazed when I encounter networking engineers who want to have a fast-converging network using Non-Stop Forwarding (which implies Graceful Restart). It’s even worse than asking for smooth-running heptagonal wheels.

As we discussed in the Fast Failover series, any decent router uses a variety of mechanisms to detect adjacent device failure:

• Physical link failure;
• Routing protocol timeouts;
• Next-hop liveliness checks (BFD, CFM…)

New Content in AWS Networking Webinar

Last week’s update session of the AWS Networking webinar covered two hours worth of new (or not-yet-covered) features, including:

• Transit Gateway Connect functionality (GRE tunnel+BGP between Transit Gateway and in-cloud SD-WAN appliances)
• AWS Private Link
• Intra-VPC static routes that you can use to send inter-subnet traffic to a BYOD security appliance
• IGMPv2 support
• Custom global accelerators
• Assigning whole IP prefixes to VM interfaces

The recordings have already been published, either as independent videos or integrated with the existing materials. Enjoy ;)

New Content in AWS Networking Webinar

Last week’s update session of the AWS Networking webinar covered two hours worth of new (or not-yet-covered) features, including:

• Transit Gateway Connect functionality (GRE tunnel+BGP between Transit Gateway and in-cloud SD-WAN appliances)
• AWS Private Link
• Intra-VPC static routes that you can use to send inter-subnet traffic to a BYOD security appliance
• IGMPv2 support
• Custom global accelerators
• Assigning whole IP prefixes to VM interfaces

The recordings have already been published, either as independent videos or integrated with the existing materials. Enjoy ;)

OMG: Democratizing Network Automation

I totally understand that entities relying on sponsors have to become creative while promoting whatever theirs sponsors want to sell, but in my opinion this is a bridge too far:

[…] explore how Gluware aims to democratize automation; that is, get you quick wins around common tasks such as configuration changes and OS updates.

Democratizing automation? Because it’s authoritarian now? By providing the abilities like configuration changes and OS updates that have been available in network management tools like CiscoWorks or SolarWinds for ages?

You know what’s really hard when automating existing networks? Figuring out how to simplify them to the point where it makes sense to automate them. Will any shrink-wrapped GUI product solve that? Of course not.

OMG: Democratizing Network Automation

I totally understand that entities relying on sponsors have to become creative while promoting whatever theirs sponsors want to sell, but in my opinion this is a bridge too far:

[…] explore how Gluware aims to democratize automation; that is, get you quick wins around common tasks such as configuration changes and OS updates.

Democratizing automation? Because it’s authoritarian now? By providing the abilities like configuration changes and OS updates that have been available in network management tools like CiscoWorks or SolarWinds for ages?

You know what’s really hard when automating existing networks? Figuring out how to simplify them to the point where it makes sense to automate them. Will any shrink-wrapped GUI product solve that? Of course not.

Must Read: BGP Private AS Range

We all know that you have to use an AS number between 64512 and 65535 for private BGP autonomous systems, right? Well, we’re all wrong – the high end of the range is 65534, and Chris Parker wrote a nice blog post explaining the reasons behind that change.

Must Read: BGP Private AS Range

We all know that you have to use an AS number between 64512 and 65535 for private BGP autonomous systems, right? Well, we’re all wrong – the high end of the range is 65534, and Chris Parker wrote a nice blog post explaining the reasons behind that change.

Video: Theoretical View of Network Addressing

After explaining the basics of (network) names, addresses and routes, I wasted a few minutes of everyone’s time discussing the theoretical aspects of layered addressing, and then got back to practical issues like address scopes, namespaces, and address provisioning.

The video ends with a simple (and unappreciated) truth: if you have a point-to-point link between two nodes you don’t need data-link-layer addresses. The consequences of that fact are left as an exercise for the viewer (or you can wait till the next video ;)

Video: Theoretical View of Network Addressing

After explaining the basics of (network) names, addresses and routes, I wasted a few minutes of everyone’s time discussing the theoretical aspects of layered addressing, and then got back to practical issues like address scopes, namespaces, and address provisioning.

The video ends with a simple (and unappreciated) truth: if you have a point-to-point link between two nodes you don’t need data-link-layer addresses. The consequences of that fact are left as an exercise for the viewer (or you can wait till the next video ;)

Should You Build or Buy a Router?

Patrik Schindler sent me an interesting comment to my Open-Source DMVPN Alternatives blog post:

Welcome to the build-or-buy dilemma, router edition.

Should You Build or Buy a Router?

Patrik Schindler sent me an interesting comment to my Open-Source DMVPN Alternatives blog post:

Welcome to the build-or-buy dilemma, router edition.

Worth Reading: Do We Need Segment Routing?

Etienne-Victor Depasquale sent me a pointer to an interesting NANOG discussion: why would we need Segment Routing. It’s well worth reading the whole thread (until it devolves into “that is not how MPLS works” arguments), which happens to be somewhat aligned with my thinking:

• SR-MPLS makes perfect sense (excluding the migration-from-LDP fun)
• SRv6 (in whatever incantation) is mostly a vendor ploy to sell new chipsets.

Enjoy!

Worth Reading: Do We Need Segment Routing?

Etienne-Victor Depasquale sent me a pointer to an interesting NANOG discussion: why would we need Segment Routing. It’s well worth reading the whole thread (until it devolves into “that is not how MPLS works” arguments), which happens to be somewhat aligned with my thinking:

• SR-MPLS makes perfect sense (excluding the migration-from-LDP fun)
• SRv6 (in whatever incantation) is mostly a vendor ploy to sell new chipsets.

Enjoy!

Graceful Restart and Other Control Plane Protocols

In the Graceful Restart 101 blog post, I promised to discuss the ugly parts of this concept in a follow-up post. It turns out we’ll need more than one; today, we’ll focus on other control plane protocols in an access network scenario.

Imagine an access router with multiple uplinks serving a bunch of non-redundantly-connected customers:

Graceful Restart and Other Control Plane Protocols

In the Graceful Restart 101 blog post, I promised to discuss the ugly parts of this concept in a follow-up post. It turns out we’ll need more than one; today, we’ll focus on other control plane protocols in an access network scenario.

Imagine an access router with multiple uplinks serving a bunch of non-redundantly-connected customers: