How can you effectively implement BGP route filtering?

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Prefix lists in BGP (Border Gateway Protocol) are used to filter routes based on their IP prefix. They offer more flexibility and efficiency compared to traditional access control lists (ACLs). In configuring prefix lists, you specify the IP address and subnet mask, allowing for the matching of specific network prefixes. You can also define sequence numbers for easier management and modification. When applied to BGP, prefix lists control route advertisement and acceptance, crucial for managing routing policies and preventing the propagation of unwanted routes.

I once used route maps to filter BGP routes based on AS path. A customer was receiving a lot of unwanted traffic from a particular AS, and I was able to block all routes from that AS with a route map. This significantly improved their network performance. In my experience, route maps are a powerful tool for filtering BGP routes. They can be used to block unwanted traffic, prioritize certain routes, or modify the attributes of routes. I've found them helpful for troubleshooting BGP problems and improving network performance. One thing that's helpful is to use route maps to create a consistent set of rules for filtering BGP routes. This can help prevent routing loops and ensure that all traffic is routed consistently.

Route maps in BGP provide a highly granular and versatile way to filter routes. They act like an "if-then" conditional statement, allowing network administrators to set various criteria for route filtering and modification. Route maps can match on multiple attributes like prefix lists, AS paths, and communities, and can set attributes like local preference or MED (Multi-Exit Discriminator). They are particularly useful for complex routing policies where multiple conditions and actions are required for precise route control.

AS path filters can be used to block routes from specific ASes, or routes with specific AS paths. They can also be used to filter routes based on the length of the AS path. One way to use AS path filters is to create a prefix list that contains all of the routes that you want to advertise. Then, you can use an AS path filter to block any routes that are not in the prefix list. This can help to ensure that you are only advertising the routes that you want to advertise.

AS path filtering is a method to permit or deny routes based on the AS (Autonomous System) path attribute. This is useful in scenarios where routes from specific ASes need to be accepted or rejected. In BGP, regular expressions are often used to match specific patterns in the AS path. For example, you can deny routes originating from a specific AS or those that have traversed through certain ASes. This filtering is critical for implementing routing policies based on business relationships and for security purposes to prevent route leaks and hijacks. Of course there is not enough space here to talk about this feature but happy to help if you want to ping me.

I’ll share my way to organize my comm: First at all, mark the incoming prefixes based on its content using a format {ASN:CRRCCSE} where: C = Category (1=internal, 2=IPT, 3=IX, 4=PNI, 5=CDN, 6=Customer) RR = Region/State (1=Brazil, 1=SP, 2=MG, 3=RJ, 4=CE) CC = Content (NTT, Cogent, IX.br, AMS-IX, Amazon, Akamai etc..– needs match category). SE = Sequential (00=all, 01=first connection, 2, 3..) For example, 65100:4140300 represent: all prefixes I’ve learned from a PNI (4) in Fortaleza/BR (14) that I have with Amazon (03) on the 1o router (00). After all content has been marked, it's easier to handle: If the customer want to receiver only IX/regional traffic (to avoid latency) in Sao Paulo IX(01) I just match ASN:3110100 on export policy

I once used community filters to solve a network problem at work. I created a filter with a name that matched the group of routes I wanted to exclude. Then, I added the filter value to the routes I wanted to keep. This ensured that only the desired routes were shared with my BGP peers, preventing any further issues. Community filters are very useful for managing BGP routes. They allow you to filter out unnecessary routes, avoid advertising routes to specific peers, and implement different policies for different route groups. When using community filters, it's helpful to establish a naming convention. For example, you can use the format <name>-<community value>. This makes it easier to track and understand your filters.

Community filters in BGP leverage the BGP community attribute, which is a tag that can be applied to routes. These tags allow for grouping routes into communities for easier management. By using community filters, routes can be accepted or denied based on their assigned community value. This method is highly effective for implementing routing policies across large networks or with multiple BGP peers, as it simplifies the management and application of policies based on the community tags assigned to routes. These are used for example In AWS with DX (Direct Connect) and Azure with Expressroute, they are useful ways to optimise traffic/routing behaviours.

Distribute lists in BGP are used to filter routing information based on access control lists (ACLs). They can be applied to inbound or outbound route updates. While less flexible than route maps or prefix lists, distribute lists are useful for simple filtering based on source or destination IP addresses. They are often used in conjunction with other filtering mechanisms, like route maps, to provide an additional layer of route control.

Filter lists in BGP are specifically used to control AS path filtering. Unlike the regular AS path filters that use regular expressions, filter lists are based on predefined AS path access lists. They offer a straightforward method to permit or deny routes based on the AS path attribute, which is crucial for controlling the flow of BGP updates based on the path routes have traversed through different ASes.

We use these kind of filters a lot. It′s pretty nice and simple to filter also more specific routes. If you don′t want to specify exact prefix length, one can use route-filter-list with 'orlonger' type of statement so it allows you to receive/advertise more precise route ie. host routes not just prefix lenght /24 etc.

Used filter lists to block rogue BGP speaker from advertising routes into our network. Filter lists are useful for controlling BGP traffic, preventing rogue speakers, filtering out unwanted routes, and controlling routes from neighbors. Create separate filter lists for each purpose.

There have been so many discussions around this topic, which has happened for quite a long time. There are several RFCs, BCPs, and other typical "standards" and ideas that promote what we should be doing to prevent route leaks and prefix hijacks from happening, in addition to reducing the landscape of issues like DDoS amplification and other types of incidents. So, I think everyone should follow the MANRS Implementation Guide. MANRS stands for "Mutually Agreed Norms for Routing Security," a global initiative that helps reduce the most common routing threats on the Internet. It is a MUST-DO deal for every Autonomous System out there. Check for its implementation guide! Have you yet to implement all of it? You are making a huge mistake!