A few weeks ago, Daniel posted a piece about using different underlay and overlay protocols in a data center fabric. He says:
There is nothing wrong with running BGP in the overlay but I oppose to the argument of it being simpler.
One of the major problems we often face in network engineering—and engineering more broadly—is confusing that which is simple with that which has lower complexity. Simpler things are not always less complex. Let me give you a few examples, all of which are going to be controversial.
From the question pile: Route servers (as opposed to route reflectors) don’t change anything about a BGP route when re-advertising it to a peer, whether iBGP or eBGP. Why don’t route servers cause routing loops (or other problems) in a BGP network?
Route servers are often used by Internet Exchange Points (IXPs) to distribute routes between connected BGP speakers. BGP route servers
- Don’t change anything about a received BGP route when advertising the route to its peers (other BGP speakers)
- Don’t install routes received through BGP into the local routing table
Shouldn’t using route servers in a network—pontentially, at least—cause routing loops or other BGP routing issues?
While RFC9199 (are we really in the 9000’s?) is targeted at large-scale DNS deployments–specifically root zone operators–so it might seem the average operator won’t find a lot of value here.
This is, however, far from the truth. Every lesson we’ve learned in deploying large-scale DNS root servers applies to any other large-scale user-facing service. Internally deployed DNS recursive servers are an obvious instance, but the lessons here might well apply to a scheduling, banking, or any other multi-user application accessed from a lot of places by a lot of different users. There are some unique points in DNS, such as the relatively slower pace of database synchronization across nodes, but the network-side lessons can still be useful for a lot of applications.
Have you ever taught a kid to ride a bike? Kids always begin the process by shifting their focus from the handlebars to the pedals, trying to feel out how to keep the right amount of pressure on each pedal, control the handlebars, and keep moving … so they can stay balanced. During this initial learning phase, the kid will keep their eyes down, looking at the pedals, the handlebars, and . . . the ground.
After some time of riding, though, managing the pedals and handlebars are embedded in “muscle memory,” allowing them to get their head up and focus on where they’re going rather than on the mechanical process of riding. After a lot of experience, bike riders can start doing wheelies, or jumps, or off-road riding that goes far beyond basic balance.
Network engineer—any kind of engineering, really—is the same way.
How do you balance loyalty to yourself and loyalty to the company you work for?
This might seem like an odd question, but it’s an important component of work/life balance many of us just don’t think about any longer because, as Pete Davis says in Dedicated, we live in a world of infinite browsing. We’re afraid of sticking to one thing because it might reduce our future options. If we dedicate ourselves to something bigger than ourselves, then we might lose control of our direction. In particular, we should not dedicate ourselves to any single company, especially for too long.
My video on BGP convergence elicited a lot of . . . feedback, mainly concerning the difference between convergence in a data center fabric and convergence in the DFZ. Let’s begin here—BGP hunt and the impact of the MRAI are very real in the DFZ. Withdrawing a route can take several minutes.
What about the much more controlled environment of a data center fabric?
Several folks pointed out that the MRAI is often set to 0 in DC fabrics (and many implementations by default). Further, almost all implementations will use an MRAI of 0 for the first received update, holding the second and subsequent advertisements by the MRAI. Several folks also pointed out that all the paths through a DC fabric are the same length, so the second part of the equation is also very small.
These are good points—how do they impact BGP convergence? Let’s use the network below, a small slice of a five-stage butterfly fabric, to think it through. Assume every router is in a different AS, so all the peering sessions are eBGP.
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.
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—
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—
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: