Next Hops of BGP Routes Reflected by Arista EOS

Imagine a suboptimal design in which:

  • A BGP route reflector also servers as an AS edge (PE) router1;
  • You want to use next-hop-self on AS edge routers.

Being exposed to Cisco IOS for decades, I considered that to be a no-brainer. After all, section 10 of RFC 4456 is pretty specific:

In addition, when a RR reflects a route, it SHOULD NOT modify the following path attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED.

Arista EOS is different – a route reflector happily modifies NEXT_HOP on reflected routes (but then, did you notice the “SHOULD NOT” wording?2)

Read more …

Next Hops of BGP Routes Reflected by Arista EOS

Imagine a suboptimal design in which:

  • A BGP route reflector also servers as an AS edge (PE) router1;
  • You want to use next-hop-self on AS edge routers.

Being exposed to Cisco IOS for decades, I considered that to be a no-brainer. After all, section 10 of RFC 4456 is pretty specific:

In addition, when a RR reflects a route, it SHOULD NOT modify the following path attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED.

Arista EOS is different – a route reflector happily modifies NEXT_HOP on reflected routes (but then, did you notice the “SHOULD NOT” wording?2)

Read more …

2 ways to remove duplicate lines from Linux files

There are many ways to remove duplicate lines from a text file on Linux, but here are two that involve the awk and uniq commands and that offer slightly different results.Remove duplicate lines with awk The first command we'll examine in this post is a very unusual awk command that systematically removes every line in the file that is encountered more than once. It leaves the first instance of the line intact, but "remembers" it and removes any duplicates encountered afterwards.Here's an example. Initially, the file looks like this:To read this article in full, please click here

2 ways to remove duplicate lines from Linux files

There are many ways to remove duplicate lines from a text file on Linux, but here are two that involve the awk and uniq commands and that offer slightly different results.Remove duplicate lines with awk The first command we'll examine in this post is a very unusual awk command that systematically removes every line in the file that is encountered more than once. It leaves the first instance of the line intact, but "remembers" it and removes any duplicates encountered afterwards.Here's an example. Initially, the file looks like this:To read this article in full, please click here

Hedge 125: Brooks Westbrook and DC Fabric Design

DC fabric design is more of an art than a science—a lot of factors come into play, such as future growth, lifecycle management, security, and costs. How can network engineers balance these various factors—how do they even know what questions to ask? Brooks Westrbook joins Tom Ammon and Russ White to discuss three- and five-stage DC fabric design, OPEX, CAPEX, and other topics on this episode of the Hedge.

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OSPF Load Balancing

OSPF Load Balancing is to place multiple next-hops into the Routing and Forwarding table for a given IP destination prefix. In this post, we will look at OSPF Load Balancing, OSPF Load Sharing, OSPF ECMP, OSPF UCMP, where we should use it, where we shouldn’t use it, and what can be dangerous if we have OSPF Load balancing will be explained.

OSPF Equal Cost Load Balancing – OSPF ECMP

What is OSPF Equal Cost Load Balancing let’s have a look at the below topology and let’s try to understand?

OSPF ECMP

In the above topology, the 192.168.0.0/24 network is connected to Router D.

As a link-state routing protocol, OSPF routers in the network would know that the 192.168.0.0/24 subnet is connected to Router D.

And they would run SPF/Dijkstra algorithm to calculate the shortest path to this destination.

In the above topology, Interface costs are shown.

When we look at Router A to 192.168.0.0/24 subnet, we have two paths. A-B-D and A-C-D.

Both of the paths’ total cost is 10+10 = 20.

Thus, Router A can do load balancing for that destination prefix.

When OSPF has two paths, we don’t need to Continue reading

How To Use Grep + Regex To Match Non-200 HTTP Status Codes In Apache Server Logs

When parsing Apache web server logs on Linux, I find it interesting to monitor access requests resulting in HTTP status codes other than 200s. An HTTP status code in the 200s mean the request was successful, and hey–that’s boring.

I want to see the requests that my dear Apache instance is upset about. So the question becomes…how do I filter the logs to show me every entry that doesn’t have a status code in the 200s?

Let’s back our way into this. We’ll start with the answer, then explain how we got there.

The Answer

This CLI incantation will get the job done.

sudo grep -E '\" [1345][01235][0-9] [[:digit:]]{1,8} \"' /var/log/apache2/access.log

If you’d like to watch the log entries scroll by in real time, try this.

sudo tail -f /var/log/apache2/access.log | grep -E '\" [1345][01235][0-9] [[:digit:]]{1,8} \"'

Comprehending The Regex

Let’s focus on the regular expression (regex) grep is using to find the matches. In plain English, the grep utility is using an extended -E regex to display all lines in the file /var/log/apache2/access.log matching the regex.

The regex portion of the command is as follows.

'\" [1345][01235][0-9] [[:digit:]]{1,8} \"'

The regex is enclosed in single quotes Continue reading

BGP AS Path Prepending

BGP AS Path Prepending or BGP prepend is a common technique for incoming path manipulating. When we want to engineer the traffic coming from another BGP AS to our BGP AS, BGP AS prepending is one of the most common mechanisms. There are cases BGP AS Prepend doesn’t work and shouldn’t be used as well, and in this post, we will look at them too by using the below topology.

bgp as path prepending

In the above topology, we have two BGP Autonomous Systems. AS 200 is Customer BGP AS, and AS 100 is Provider BGP AS.

As a customer, AS 200 wants AS100 to send the traffic over the left path as a Primary path and the right path as a backup path as is depicted in the above topology.

BGP AS Path Prepend

When we want to have Primary and Backup Paths as it is depicted in the above topology. BGP AS Path Prepending technique is used to influence upstream BGP Autonomous Systems’ decision.

BGP Prepend means, adding our BGP AS to the AS-path multiple times. In the above topology, 10.0.10.0/24 network’s BGP AS 200 is advertised with 3 AS prepend. By default when the prefix is advertised to Continue reading

7 emerging network jobs that could boost your career

The relatively stable world of enterprise networking has undergone quite a bit of upheaval over the past few years. As a result, networking professionals with traditional job titles have assumed new responsibilities, and entirely new job titles have emerged.Key trends reshaping the jobs of network professionals include increased adoption of cloud services; the push for more automation of business processes; and the rise of technologies such as software-defined networking (SDN), SD-WAN, Internet of Things (IoT) , secure access service edge (SASE), Zero Trust Network Access (ZTNA) and edge computing.To read this article in full, please click here

7 emerging network jobs that could boost your career

The relatively stable world of enterprise networking has undergone quite a bit of upheaval over the past few years. As a result, networking professionals with traditional job titles have assumed new responsibilities, and entirely new job titles have emerged.Key trends reshaping the jobs of network professionals include increased adoption of cloud services; the push for more automation of business processes; and the rise of technologies such as software-defined networking (SDN), SD-WAN, Internet of Things (IoT) , secure access service edge (SASE), Zero Trust Network Access (ZTNA) and edge computing.To read this article in full, please click here

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