BGP Policy (Part 7)

9 May 2022 |

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

There are cases where an operator does not traffic to be forwarded to them through some specific AS, whether directly connected or multiple hops away. For instance, AS65001 and AS65005 might be operated by companies in politically unfriendly nations. In this case, AS65001 may be legally required to reject traffic that has passed through the nation in which AS65005 is located. There are at least three mechanisms in BGP that are used, in different situations, to enforce this kind of policy.

BGP Policy (Part 6)

3 May 2022 | Comments Off on BGP Policy (Part 6)

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

In this post I’m going to cover local preference via communities, longer prefix match, and conditional advertisement from the perspective of AS65001 in the following network—

BGP Policies (Part 5)

25 April 2022 | Comments Off on BGP Policies (Part 5)

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

In this post I’m going to cover AS Path Prepending from the perspective of AS65001 in the following network—

BGP Policies (Part 4)

4 April 2022 | Comments Off on BGP Policies (Part 4)

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

In this post, I’ll cover the first of a few ways to give surrounding autonomous systems a hint about where traffic should enter a network. Note this is one of the most vexing problems in BGP policy, so there will be a lot of notes across the next several posts about why some solutions don’t work all that well, or when they will and won’t work.

There are at least three reasons an operator may want to control the point at which traffic enters their network, including:

BGP Policies (Part 2)

14 March 2022 | Comments Off on BGP Policies (Part 2)

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

There are many reasons an operator might want to select which neighboring AS through which to send traffic towards a given reachable destination (for instance, 100::/64). Each of these examples assumes the AS in question has learned multiple paths towards 100::/64, one from each peer, and must choose one of the two available paths to forward along. This post wil consider selecting an exit point from the perspective of two more autonomous systems.

BGP Policies (part 1)

7 March 2022 |

At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I’m going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

Quality is (too often) the missing ingredient

3 January 2022 | Comments Off on Quality is (too often) the missing ingredient

Software Eats the World?

I’m told software is going to eat the world very soon now. Everything already is, or will be, software based. To some folks, this sounds completely wonderful, but—leaving aside the privacy issues—I still see an elephant in the room with this vision of the future.

Quality.

Let me give you some recent examples.

First, ceiling fans. Modern ceiling fans, in case you didn’t know, don’t rely on the wall switch and pull chains. Instead, they rely on remote controls. This is brilliant—you can dim the light, change the speed of the fan, etc., from a remote control. No unsightly chains hanging from the ceiling.

Thoughts on Auto Disaggregation and Complexity

15 November 2021 | Comments Off on Thoughts on Auto Disaggregation and Complexity

Way in the past, the EIGRP team (including me) had an interesting idea–why not aggregate routes automatically as much as possible, along classless bounds, and then deaggregate routes when we could detect some failure was causing a routing black hole? To understand this concept better, consider the network below.

Keith’s Law (1)

28 September 2021 | Comments Off on Keith’s Law (1)

I sometimes reference Keith’s Law in my teaching, but I don’t think I’ve ever explained it. Keith’s Law runs something like this:

Any large external step in a system’s capability is the result of many incremental changes within the system.

Thoughts on the Collapsed Spine

21 September 2021 |

One of the designs I’ve been encountering a lot of recently is a “collapsed spine” data center network, as shown in the illustration below.