MARCO JANSEN
Okay, let's delve into the concept of Marco Jansen routing in BGP. This is a lesser-known but powerful technique for influencing routing decisions and optimizing network performance. I'll break it down with explanations, examples, step-by-step reasoning, and practical applications.
Marco Jansen routing, named after the network engineer who popularized the concept, is a method of using BGP communities to control the "hot potato" or "cold potato" routing behavior within an Autonomous System (AS) or across multiple ASes. It's essentially a way to influence where traffic exits your AS (or which AS you use to transit to another AS).
The core mechanism is the use of BGP communities to signal the egress preference to adjacent ASes. Here's how it works:
1. Defining BGP Communities: You define specific BGP communities, which are essentially tags you attach to routes. These communities have a pre-agreed-upon meaning with your neighboring ASes. For example:
`65001:100` might mean "Prefer this egress point" (for a specific AS)
`65001:200` might mean "Less preferred egress point" (for a specific AS)
`65001:300` might mean "Do not use this egress point" (for a specific AS)
(Note: `65001` here is an example AS number. You'd use your own AS number or a well-defined community based on agreement with your peer.)
2. Applying Communities to Routes: You use route maps (or similar mechanisms depending on your router vendor) to apply these communities to specific prefixes. The route map will match certain prefixes and then set (or append) the relevant BGP communities.
3. Advertising the Routes with Communities: Your router advertises these routes with the attached communities to your BGP neighbors.
4. Neighboring AS Interpretation: Your neighboring ASes have been configured to understand the meaning of these communities. Based on the communities they receive, they adjust their BGP best path selection process to prefer or avoid the routes you've advertised. This typically involves matching those communities in route-maps on their side and adjusting the `local-preference` or `MED` (Multi-Exit Discriminator) values.
Let's say you have AS 65001. You have two egress points to AS 65002: Router A and Router B. You want to influence AS 65002 to use Router A for traffic destined for network `192.0.2.0/24`.
1. Define Communities: In AS 65001, you define:
`65001:100` = "Prefer AS 65001's Router A for egress to `192.0.2.0/24`"
2. Configure Route Map (AS 65001): On Router A in AS 65001:
```
route-map MJ-TO-AS65002 permit 10
match ip address prefix-list PL-192.0.2.0
set community 65001:100 additive
!
ip prefix-list PL-192.0.2.0 seq 5 permit 192.0.2.0/24
!
router bgp 65001
neighbor route-map MJ-TO-AS65002 out
```
This configuration applies the community `65001:100` to any route matching the prefix `192.0.2.0/24` and advertises this to AS 65002.
3. Configure Route Map (AS 65002): On Router A in AS 65002 (the neighbor receiving the advertisement):
```
route-map MJ-FROM-AS65001 permit 10
match community MJ-PREF-A
set local-preference 150
!
ip community-list expanded MJ-PREF-A permit "^65001:100$"
!
router bgp 65002
neighbor route-map MJ-FROM-AS65001 in
```
This configuration increases the `local-preference` of any route received from AS 65001 that has the community `65001:100`. Higher `local-preference` means it's preferred within the AS.
4. Result: AS 65002 will now prefer Router A in AS 65001 for reaching `192.0.2.0/24`.
BGP has a well-defined best path selection algorithm. Key attributes that influence this algorithm, and which Marco Jansen routing leverages, are:
1. Weight: (Cisco specific) Local to the router. Not advertised.
2. Local Preference: Advertised within the AS. Higher is better. This is the most common attribute modified by Marco Jansen.
3. AS-Path Length: Shorter is generally better.
4. Origin Type: IGP < EGP < Incomplete (Network Statement)
5. MED (Multi-Exit Discriminator): Lower is better. This is an attribute advertised between ASes. It's less reliable than `local-preference` because some ASes ignore it.
6. External BGP (eBGP) vs. Internal BGP (iBGP): eBGP is preferred over iBGP.
7. IGP Cost to the BGP Next Hop: Lower IGP cost is better.
8. BGP Router ID: Lower Router ID is preferred (used as a tie-breaker).
Marco Jansen routing typically works by influencing `local-preference` (within an AS) or `MED` (between ASes) using communities, thereby altering the best path selection process.
Marco Jansen routing is a useful tool for influencing BGP routing decisions by using BGP communities. It allows network operators to steer traffic through specific paths, optimize network performance, and enforce policies. However, it's crucial to remember that it requires agreement between participating ASes, careful configuration, and thorough monitoring to avoid routing issues. It is often a "lightweight" approach compared to more complex traffic engineering techniques, but can be very effective when used appropriately.
What is Marco Jansen Routing? (The Core Idea)
Marco Jansen routing, named after the network engineer who popularized the concept, is a method of using BGP communities to control the "hot potato" or "cold potato" routing behavior within an Autonomous System (AS) or across multiple ASes. It's essentially a way to influence where traffic exits your AS (or which AS you use to transit to another AS).
Hot Potato Routing (Minimize internal hops): In a hot potato scenario, you try to get the traffic out of your AS as quickly as possible, even if it means it might take a longer or potentially less efficient path to the final destination outside your AS. You hand it off (like a hot potato) to the next hop as soon as you can.
Cold Potato Routing (Minimize external hops): In a cold potato scenario, you keep the traffic within your AS for as long as possible, optimizing the path within your own network, before handing it off to the next AS. You hold onto it (like a cold potato) until you have a good path to get it to its destination.
How Marco Jansen Routing Works: Using BGP Communities
The core mechanism is the use of BGP communities to signal the egress preference to adjacent ASes. Here's how it works:
1. Defining BGP Communities: You define specific BGP communities, which are essentially tags you attach to routes. These communities have a pre-agreed-upon meaning with your neighboring ASes. For example:
`65001:100` might mean "Prefer this egress point" (for a specific AS)
`65001:200` might mean "Less preferred egress point" (for a specific AS)
`65001:300` might mean "Do not use this egress point" (for a specific AS)
(Note: `65001` here is an example AS number. You'd use your own AS number or a well-defined community based on agreement with your peer.)
2. Applying Communities to Routes: You use route maps (or similar mechanisms depending on your router vendor) to apply these communities to specific prefixes. The route map will match certain prefixes and then set (or append) the relevant BGP communities.
3. Advertising the Routes with Communities: Your router advertises these routes with the attached communities to your BGP neighbors.
4. Neighboring AS Interpretation: Your neighboring ASes have been configured to understand the meaning of these communities. Based on the communities they receive, they adjust their BGP best path selection process to prefer or avoid the routes you've advertised. This typically involves matching those communities in route-maps on their side and adjusting the `local-preference` or `MED` (Multi-Exit Discriminator) values.
Step-by-Step Example
Let's say you have AS 65001. You have two egress points to AS 65002: Router A and Router B. You want to influence AS 65002 to use Router A for traffic destined for network `192.0.2.0/24`.
1. Define Communities: In AS 65001, you define:
`65001:100` = "Prefer AS 65001's Router A for egress to `192.0.2.0/24`"
2. Configure Route Map (AS 65001): On Router A in AS 65001:
```
route-map MJ-TO-AS65002 permit 10
match ip address prefix-list PL-192.0.2.0
set community 65001:100 additive
!
ip prefix-list PL-192.0.2.0 seq 5 permit 192.0.2.0/24
!
router bgp 65001
neighbor
```
This configuration applies the community `65001:100` to any route matching the prefix `192.0.2.0/24` and advertises this to AS 65002.
3. Configure Route Map (AS 65002): On Router A in AS 65002 (the neighbor receiving the advertisement):
```
route-map MJ-FROM-AS65001 permit 10
match community MJ-PREF-A
set local-preference 150
!
ip community-list expanded MJ-PREF-A permit "^65001:100$"
!
router bgp 65002
neighbor
```
This configuration increases the `local-preference` of any route received from AS 65001 that has the community `65001:100`. Higher `local-preference` means it's preferred within the AS.
4. Result: AS 65002 will now prefer Router A in AS 65001 for reaching `192.0.2.0/24`.
Why This Works (BGP Best Path Selection)
BGP has a well-defined best path selection algorithm. Key attributes that influence this algorithm, and which Marco Jansen routing leverages, are:
1. Weight: (Cisco specific) Local to the router. Not advertised.
2. Local Preference: Advertised within the AS. Higher is better. This is the most common attribute modified by Marco Jansen.
3. AS-Path Length: Shorter is generally better.
4. Origin Type: IGP < EGP < Incomplete (Network Statement)
5. MED (Multi-Exit Discriminator): Lower is better. This is an attribute advertised between ASes. It's less reliable than `local-preference` because some ASes ignore it.
6. External BGP (eBGP) vs. Internal BGP (iBGP): eBGP is preferred over iBGP.
7. IGP Cost to the BGP Next Hop: Lower IGP cost is better.
8. BGP Router ID: Lower Router ID is preferred (used as a tie-breaker).
Marco Jansen routing typically works by influencing `local-preference` (within an AS) or `MED` (between ASes) using communities, thereby altering the best path selection process.
Practical Applications
Traffic Engineering: Directing traffic through specific links or routers to avoid congestion, optimize bandwidth utilization, or meet service level agreements (SLAs).
Cost Optimization: Routing traffic through cheaper or more cost-effective transit providers. You might use one provider for most traffic but prefer a different provider for traffic to a specific region.
Redundancy and Failover: Ensuring that traffic can quickly failover to a backup path if the primary path becomes unavailable. You can dynamically adjust community settings to steer traffic away from a failed link.
Content Delivery Networks (CDNs): Directing users to the closest or most appropriate CDN server based on their location or network conditions.
Peering Agreements: Honoring peering agreements by sending traffic to specific peers when appropriate.
Controlling Egress Points: In scenarios with multiple exit points, you can use communities to influence the choice of the egress point based on destination prefixes. This can be used to enforce policies or optimize performance.
Important Considerations and Best Practices
Agreement is Essential: Marco Jansen routing requires agreement between the participating ASes. You must clearly define the meaning of the communities and how they will be interpreted. Lack of coordination will lead to routing problems.
Documentation is Key: Thoroughly document the communities you are using and their meaning. This documentation should be shared with your peering partners.
Filtering: Implement proper filtering to prevent malicious or unintentional community manipulation. Only accept communities from trusted sources.
Monitoring: Monitor your network to ensure that your Marco Jansen routing policies are working as expected. Look for unexpected routing changes or traffic patterns.
Scalability: As your network grows, managing a large number of communities can become complex. Consider using more sophisticated routing policies and automation tools to simplify community management.
Security: Be aware that attackers could potentially manipulate BGP communities to redirect traffic. Implement appropriate security measures to protect your network.
Alternatives: Consider other traffic engineering techniques, such as BGP MEDs or more advanced tools like Segment Routing, depending on your network requirements and capabilities. Marco Jansen is a simpler, but sometimes less flexible, option.
Advantages of Marco Jansen Routing:
Relatively Simple to Implement: Compared to some other traffic engineering techniques, Marco Jansen routing is relatively straightforward to configure.
Flexible: It provides a flexible way to influence routing decisions based on a variety of factors.
Scalable: While management can get complex with a large number of communities, it's generally scalable.
Disadvantages of Marco Jansen Routing:
Requires Agreement: This is the biggest limitation. It necessitates coordination with neighboring ASes, which can be challenging.
Potential for Misconfiguration: Incorrectly configured communities can lead to routing problems.
Less Precise than Other Techniques: Compared to techniques like Segment Routing, it offers less precise control over traffic paths.
Security Considerations: BGP communities can be manipulated by attackers.
In Summary
Marco Jansen routing is a useful tool for influencing BGP routing decisions by using BGP communities. It allows network operators to steer traffic through specific paths, optimize network performance, and enforce policies. However, it's crucial to remember that it requires agreement between participating ASes, careful configuration, and thorough monitoring to avoid routing issues. It is often a "lightweight" approach compared to more complex traffic engineering techniques, but can be very effective when used appropriately.
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