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Unequal-Cost Multipath with BGP DMZ Link Bandwidth

In the previous blog post in this series, I described why it’s (almost) impossible to implement unequal-cost multipathing for anycast services (multiple servers advertising the same IP address or range) with OSPF. Now let’s see how easy it is to solve the same challenge with BGP DMZ Link Bandwidth attribute.

I didn’t want to listen to the fan noise generated by my measly Intel NUC when simulating a full leaf-and-spine fabric, so I decided to implement a slightly smaller network:

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Feedback: Azure Networking

When I started developing AWS- and Azure Networking webinars, I wondered whether they would make sense – after all, you can easily find tons of training offerings focused on public cloud services.

However, it looks like most of those materials focus on developers (no wonder – they are the most significant audience), with little thought being given to the needs of network engineers… at least according to the feedback left by one of ipSpace.net subscribers.

I have been searching online for months for any training content that go deep dive in Azure networking as we are moving to Azure currently in my company, but I didn’t find any content that explains in details the technical architectures, and all ins- and outs about Azure networking. I am so delighted that I have subscribed to ipspace.net. Keep up the good work.

Feedback: Azure Networking

When I started developing AWS- and Azure Networking webinars, I wondered whether they would make sense – after all, you can easily find tons of training offerings focused on public cloud services.

However, it looks like most of those materials focus on developers (no wonder – they are the most significant audience), with little thought being given to the needs of network engineers… at least according to the feedback left by one of ipSpace.net subscribers.

I have been searching online for months for any training content that go deep dive in Azure networking as we are moving to Azure currently in my company, but I didn’t find any content that explains in details the technical architectures, and all ins- and outs about Azure networking. I am so delighted that I have subscribed to ipspace.net. Keep up the good work.

Routing Protocols: Use the Best Tool for the Job

When I wrote about my sample katacoda hands-on lab on LinkedIn (mentioning how easy it is to set up an OSPF+BGP network), someone couldn’t resist asking:

I’m still wondering why people use two routing protocols and do not have clean redistribution points or tunnels.

Ignoring for the moment the fact that he missed the point of the blog post (completely), the idea of “using tunnels or redistribution points instead of two routing protocols” hints at the potential applicability of RFC 1925 rule 4.

Read more …

Routing Protocols: Use the Best Tool for the Job

When I wrote about my sample OSPF+BGP hands-on lab on LinkedIn, someone couldn’t resist asking:

I’m still wondering why people use two routing protocols and do not have clean redistribution points or tunnels.

Ignoring for the moment the fact that he missed the point of the blog post (completely), the idea of “using tunnels or redistribution points instead of two routing protocols” hints at the potential applicability of RFC 1925 rule 4.

Read more …

Unnumbered Ethernet Interfaces

Imagine an Internet Service Provider offering Ethernet-based Internet access (aka everyone using fiber access, excluding people believing in Russian dolls). If they know how to spell security, they might be nervous about connecting numerous customers to the same multi-access network, but it seems they have only two ways to solve this challenge:

  • Use private VLANs with proxy ARP on the head-end router, forcing the customer-to-customer traffic to pass through layer-3 forwarding on the head-end router.
  • Use a separate routed interface with each customer, wasting three-quarters of their available IPv4 address space.

Is there a third option? Can’t we pretend Ethernet works in almost the same way as dialup and use unnumbered IPv4 interfaces?

Read more …

Unnumbered Ethernet Interfaces

Imagine an Internet Service Provider offering Ethernet-based Internet access (aka everyone using fiber access, excluding people believing in Russian dolls). If they know how to spell security, they might be nervous about connecting numerous customers to the same multi-access network, but it seems they have only two ways to solve this challenge:

  • Use private VLANs with proxy ARP on the head-end router, forcing the customer-to-customer traffic to pass through layer-3 forwarding on the head-end router.
  • Use a separate routed interface with each customer, wasting three-quarters of their available IPv4 address space.

Is there a third option? Can’t we pretend Ethernet works in almost the same way as dialup and use unnumbered IPv4 interfaces?

Read more …

Single-Metric Unequal-Cost Multipathing Is Hard

A while ago we discussed whether unequal-cost multipathing (UCMP) makes sense (TL&DR: rarely), and whether we could implement it in link-state routing protocols (TL&DR: yes). Even though we could modify OSPF or IS-IS to support UCMP, and Cisco IOS XR even implemented those changes (they are not exactly widely used), the results are… suboptimal.

Imagine a simple network with four nodes, three equal-bandwidth links, and a link that has half the bandwidth of the other three:

Read more …

Single-Metric Unequal-Cost Multipathing Is Hard

A while ago, we discussed whether unequal-cost multipathing (UCMP) makes sense (TL&DR: rarely), and whether we could implement it in link-state routing protocols (TL&DR: yes). Even though we could modify OSPF or IS-IS to support UCMP, and Cisco IOS XR even implemented those changes (they are not exactly widely used), the results are… suboptimal.

Imagine a simple network with four nodes, three equal-bandwidth links, and a link that has half the bandwidth of the other three:

Read more …

Worth Reading: Azure Datacenter Switch Failures

Microsoft engineers published an analysis of switch failures in 130 Azure regions (review of the article, The Next Platform summary):

  • A data center switch has a 2% chance of failing in 3 months (= less than 10% per year);
  • ~60% of the failures are caused by hardware faults or power failures, another 17% are software bugs;
  • 50% of failures lasted less than 6 minutes (obviously crashes or power glitches followed by a reboot).
  • Switches running SONiC had lower failure rate than switches running vendor NOS on the same hardware. Looks like bloatware results in more bugs, and taking months to fix bugs results in more crashes. Who would have thought…

Worth Reading: Azure Datacenter Switch Failures

Microsoft engineers published an analysis of switch failures in 130 Azure regions (review of the article, The Next Platform summary):

  • A data center switch has a 2% chance of failing in 3 months (= less than 10% per year);
  • ~60% of the failures are caused by hardware faults or power failures, another 17% are software bugs;
  • 50% of failures lasted less than 6 minutes (obviously crashes or power glitches followed by a reboot).
  • Switches running SONiC had lower failure rate than switches running vendor NOS on the same hardware. Looks like bloatware results in more bugs, and taking months to fix bugs results in more crashes. Who would have thought…

Worth Reading: Running BGP in Large-Scale Data Centers

Here’s one of the major differences between Facebook and Google: one of them publishes research papers with helpful and actionable information, the other uses publications as recruitment drive full of we’re so awesome but you have to trust us – we’re not sharing the crucial details.

Recent data point: Facebook published an interesting paper describing their data center BGP design. Absolutely worth reading.

Just in case you haven’t realized: Petr Lapukhov of the RFC 7938 fame moved from Microsoft to Facebook a few years ago. Coincidence? I think not.

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