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Excerpt: My post a few weeks ago about the CSR 1000v made a pretty big splash – it’s clear that the industry is giving a lot of attention to IP routing within a virtual environment. No doubt, Vyatta is largely credited for this, as they’ve been pushing this idea for a long time. When Brocade announced that they were acquiring Vyatta, and Cisco announced they were working on a “Cloud Services Router”, this idea became all the more legitimate, and as you can tell from this series, it’s of particular interest to me. The overwhelming majority of virtualized deployments in place…
Virtual Routing [Part 2 - Router Redundancy in VMware vSphere]
May 7, 2013 by 4 Comments
IGP Route Multipathing
April 29, 2013 by 2 Comments
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Excerpt: In preparation for an upcoming post, I was reminded about a commonly referred to feature in most IGPs – the concept of Equal-Cost Multipath, or simply ECMP. This is the idea that multiple routes with the same cost to a remote network should get placed in the routing table alongside each other and packets should load-balance over them to use the additional available paths. After all, it’s the same cost, so why not? ECMP isn’t really talked about with EIGRP, since the metric is more complicated and routes with equal metric rarely happen, even if they are physically similar. This is…
Multi-Vendor OSPF Cost Calculations
April 22, 2013 by 3 Comments
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Excerpt: While on my current kick with virtual routing, I stumbled across an interesting concept regarding OSPF, and the flexibility that vendors have in determining the best path through an OSPF network. The following topology is what I’ve been staring at for the last few days: Pretty simple, right? There’s a single network (192.168.123.0/24) down inside each virtual host where the VMs are to sit. Each host has a router on it (one Cisco CSR 1000v and the other Vyatta Core 6.5), and both routers are OSPF neighbors with each other as well as with an upstream L3 switch. Given this topology, and knowing…
IPv6 Next-Hop Best Practices
March 21, 2013 by 4 Comments
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Excerpt: The concept of a link-local address is new to some, seeing as the term is not widely talked about in IPv4 circles, despite the fact that some folks see them daily. In IPv4, the range 169.254.1.0 through 169.254.254.255 has been reserved for this purpose. You may see this in the “ipconfig” output of a windows host that failed to pull a DHCP address. In IPv6, fe80::/10 is reserved for this purpose, though link-local addresses are always configured with a fe80::/64 prefix. The concept of a link-local address is much more heavily used in IPv6, and one very popular use case is…
A Contest of Protocols: EIGRP or OSPF?
March 18, 2013 by 1 Comment
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Excerpt: Ah, the age old question that nearly every CCNA and CCNP candidate asks of themselves and others at some point. We see a minimum of 4 routing protocols in our networking studies, more if you decide to take on the Service Provider track. What makes one routing protocol better than another? I think it’s clear why (at least mostly) these particular two protocols are different, keeping in mind that one is distance vector (yes, distance vector, not hybrid distance vector) and the other is link state. At this point, we at least have a fundamental understanding of what’s different between those…
Link-State vs. Distance Vector – The Lowdown
October 25, 2011 by 2 Comments
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Excerpt: I’ve been trying to get more into networking message boards like Networking Forum and TechExams.net lately. It’s a great way to get in touch with fellow packet lovers and gain some interesting perspectives along the way. In fact, it’s great for anyone in networking, whether you’re a hardened veteran or a newbie – there’s usually a place for you in at least one of these sites. As a result, I’ve seen quite a few posts asking about fundamental concepts, which is great because it shows that new networkers are getting out there and learning new things proactively. I’d like to address one such post…
EIGRP Unequal-Cost Load-Balancing
September 22, 2011 by Leave a Comment
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Excerpt: In a previous post, I explored the basics of IP routing, and in the process, we discovered an interesting default feature of OSPF. When there were two OSPF routes in the routing table to a network, and both routes had the same cost, the router performed load balancing between the two. Take, for instance, the following route: 172.16.2.0 [110/12] via 1.1.1.13, 00:09:24, FastEthernet0/0 [110/12] via 1.1.1.2, 00:09:24, FastEthernet0/1 In this example, every packet sent would take one of two routes. The next hop at this particular…
