Route on Aaron's Worthless Words

Summary Post - OSPF Network Statement Order and Matching

Thu, 10 Jul 2014 00:00:00 +0000

When you configure OSPF network statements, IOS orders them most-specific to least-specific then does a top-to-bottom match of the interfaces. It doesn’t matter which order you put them in, the configuration will always be ordered with the longest prefix matches first. Lab time!

I have router R1 with these interfaces.

R1#sh ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            10.0.0.1        YES manual up                    up
FastEthernet0/1            unassigned      YES unset  administratively down down
Loopback100                10.0.101.1      YES manual up                    up
Loopback200                10.2.101.1      YES manual up                    up

Let’s add the OSPF configuration where 10.0.0.0/8 is in area 2 then check what OSPF thinks is happening.

Advertising a Default Route Into EIGRP

Sun, 06 Jul 2014 00:00:00 +0000

Let’s get an IPv4 default route into EIGRP. There are a few methods to do it. I hate most of them, though. I think it will be obvious which one I like.

Here’s the lab I have set up to test everything. I want R4 to generate the default in each case.

Default Network - Candidate default. I don’t think I’ve ever used that all my years in networking, but here’s how to use it in EIGRP for a default route. You basically say “If you don’t know where to send a packet, send it to where network X lives.” We’re going to set the 192.168.1.0/24 as the default network, so, in our case X = 192.168.1.0. R4 will tag that route as a default candidate when it advertises it to the rest of the network. The config is easy but requires a classful (yes, classful) network to be configured as the default.

EIGRP Redistribution - Default Metrics of Connected and Static Routes

Thu, 19 Jun 2014 00:00:00 +0000

I wanted to do some analysis of the EIGRP topology table last night, so I fired up a small lab. I was especially interested in how external routes appear there and compare to internal entries. Like all good scientific endeavors, the whole thing got derailed when I made a realization.

Here’s the lab I set up. You can ignore the IPv6 info for this exercise.

It’s a simple little thing. All the networks you see are included in EIGRP 100 for simplicity. I limited the network statements to 192.0.2.0/24 to keep my options open. I went ahead and added Loopback100 on R3 with an address of 3.3.3.3/32 and added a redistribute connected with a route-map to get the route out in the wild. Here’s what I had.

OSPF and Loopback Interfaces

Sun, 31 Jul 2011 00:00:00 +0000

I was studying via Google+ Hangout the other day with CJ and Rob, and one of the topics that came up was that OSPFv2 advertises all loopbacks as 32-bit no matter what the configured mask is. I rarely use loopbacks outside of a lab and had no idea it did that, so I set up a quick lab to see for myself. Sure enough! That’s exactly what I saw.

Of course, being the inquisitive network guys that we are, we went on to discuss methods for making OSPF advertise the configured network instead of the single IP. The guys mentioned two methods - to redistribute the connected interfaces and to manually set the OSPF network type on the loopback. We were using IPv4 during the session, but I went back and added some IPv6 addresses and processes to compare.

Routing IPv6 with BGP - The Basics

Thu, 10 Feb 2011 00:00:00 +0000

Are you sensing a theme lately? Since we covered the basics of the main IGPs (I’m an enterprise guy, so no IS-IS comments, please.), I thought I’d try to describe the basics of advertising IPv6 routes over BGP. Yet again, we’re not going to do any route manipulation or change any of the 948284928 BGP attributes. We’re just trying to get routes exchanged.

Configuration

There’s no new version of BGP for IPv6 here. It’s the standard BGP version 4 that we’ve all been using for years, but we’re going to take advantage of the multiprotocol support (MPBGP, RFC 2858 RFC 4760). We’ll get to the differences in a second, but the first thing to do is to set up the BGP process as normal.

OSPFv3 - The Basics

Tue, 01 Feb 2011 00:00:00 +0000

A few hours ago, the last of the IPv4 addresses were allocated by IANA. Now’s the time to learn more about IPv6! Yesterday, I posted about EIGRP for IPv6, so I think I’ll continue the trend by introducing OSPFv3, which is the IPv6 implementation of OSPF. As always, I’m using Cisco routers here. Just as yesterday, this is just a guide to the absolutely basics; if you want to do some funky OSPF magic, you won’t find it here - perhaps in time, though.

EIGRP for IPv6 - The Basics

Mon, 31 Jan 2011 00:00:00 +0000

I’m not going to go all out like Jeremy over at Packetlife.net has, but I’m going to start to discuss a few IPv6 topics. In time (like in September when APNIC runs out of IPv4 addresses), I’m sure I’ll ramp up the IPv6 talk, but let’s start easy and get EIGRP for IPv6 up and running.

Configuration

There are quite a few differences between EIGRP for IPv6 (yes, that’s an official name) and the IPv4 version. First of all, all IPv6 routing is disabled by default on a Cisco router, so, if you’re doing any routing in IPv6, you’ll want to enable it or risk smashing your head into the desk trying to figure out what’s going on.

Tagging External Routes in EIGRP

Fri, 03 Dec 2010 00:00:00 +0000

EIGRP allows you to tag external routes. That is, any route redistributed into EIGRP can be tagged with a numeric descriptor from 0 to 4294967295.

ROUTE - Epic Win!

Mon, 19 Jul 2010 00:00:00 +0000

Woohoo! I passed the ROUTE test this morning. That means I’m done with the CCNP track! :)

If you remember, I took it over a week ago and had some bad luck on it. Alright, bad luck is the wrong phrase. I didn’t study enough and failed it. This time, though, I had a special weapon on my side - the ROUTE Foundations book. I haven’t used the Foundations books before, but, I saw some tweets about this one, so I picked it up off of Safari. In just a couple pages, I realized that I was reading the answers to several questions directly out of the book. It was amazing. I only studied my weak points and wound up with 144 more points than I did last time. I can’t say that was entirely because of the book, but I must say it was a big reason.

ROUTE Notes - Further IGP Redistribution

Sun, 18 Jul 2010 00:00:00 +0000

As always, corrections are requested.

Study Questions

I’ve got IGRP and EIGRP both configured with the same AS number. What’s special about this configuration?

If both use the same AS number, then they automatically redistribute their routes into each other without using the redistribute command.

When redistributing one IGP into another, where’s a good place to filter routes?

There’s no one good place, but at the router(s) that’s doing the redistribution is a good start. There’s no need to send an IGP a bunch of routes it doesn’t need.

ROUTE Notes - Even More IGP Redistribution

Sat, 17 Jul 2010 00:00:00 +0000

I didn’t do so well on IGP redistribution the last time out, so here’s some more stuff to study. As always, feel free to correct.

Study Questions

What three things are needed to be able to redistribute one routing protocol into another?

1. One or more links into each routing protocol 2. A proper, working config for each protocol 3. The addition of the redistribute command to one or more of the protocols

ROUTE - Epic Fail (#1?)

Thu, 08 Jul 2010 00:00:00 +0000

I took the ROUTE test today and failed like I usually do. That makes me 3-4 on these P-level tests if you’re scoring at home. Don’t worry, though. I’m not giving up. :)

In atypical fashion, I must say that the ROUTE test was a good test. Let me say that again. The ROUTE test was a good test. I said good, though…not great. There were a few problems with it that I’ll get to, but, overall, this is the best test I’ve ever taken for a Cisco cert. The questions were very well-written and there were no obvious omissions or wrong details. I failed this test because I simply didn’t put in enough work.

ROUTE Notes - Controlling BGP

Tue, 06 Jul 2010 00:00:00 +0000

Corrections, please. I skipped a bunch of BGP intro stuff to get to the juicy center. I’ll see if I can come back later and finish the other parts for posterity.

Study Notes

Is BGP route selection a controversial subject?

Yes. If you ask 1000 network guys the best way to influence BGP, you’ll probably get 1000 different answers.

At what position in the PA list of a BGP update do you find the weight attribute?

You don’t. Weight is a Cisco-proprietary thing.

ROUTE Notes - Branch Office Routing

Mon, 05 Jul 2010 00:00:00 +0000

Corrigeme, por favor.

Study Notes

What do IPSec tunnels give you when a branch office is on a broadband connection?

Privacy through encryption Authentication of the remote peer through ISAKMP Delivery of private data over the public Internet

What do you need to configure to get your branch router talking to the Internet?

ISP connection configuration such as PPPoE or PPPoA DHCP server configuration for internal users NAT Firewall services like inspection and filtering

ROUTE Notes - Implementing IPv6 in an IPv4 Network

Sun, 04 Jul 2010 00:00:00 +0000

Study Questions

Your boss says that ever host in the network needs to be converted over to IPv6 by the end of the day. Which of multipoint tunnels, point-to-point tunnels, or native IPv6 would be the most appropriate to use to help with that conversion?

Native IPv6

The engineering department wants to permanently use IPv6 on their test boxes in two offices. Which of multipoint tunnels, point-to-point tunnels, or native IPv6 would be the most appropriate to use?

Point-to-point tunnels

ROUTE Notes - Routing IPv6

Wed, 30 Jun 2010 00:00:00 +0000

Study Questions

Why would anyone develop a version of RIP that supports IPv6?

I have no idea. Boredom, maybe. Whatever the case, it works just like RIPv2, which is pretty scary.

In EIGRP for IPv4, there are several requirements for two routers to neighbor up. Which of those is not true for EIGRP for IPv6?

The two routers don’t need to be in the same subnet. The concept of the link local address takes care of that need since neighbors always share a common medium like an Ethernet segment or a serial link.

ROUTE Notes - Intro to IPv6

Tue, 29 Jun 2010 00:00:00 +0000

Study Notes

Exactly how big is an IPv6 address?

It’s 128 bits long.

This shouldn’t be on the test, but how many unique addresses is that?

That’s 2^128 or a “3” with 38 zeros after it. That’s also 2^95 addresses for each person on earth.

Surely we’re not writing in binary, are we?

No way. IPv6 uses 32 hex characters. Each character is 4 bits, so we wind up with 128 bits of data.

ROUTE Notes - PBR and IP SLA

Thu, 24 Jun 2010 00:00:00 +0000

Feel free to correct.

Study Questions

What’s the most primitive way to get traffic destined to a single host to use a different path than your dynamic IGP dictates?

Use a static route.

What’s the most primitive way to get traffic sourced from a single host to use a different path than your dynamic IGP dictates?

Use policy-based routing (PBR).

What’s the most primitive way to get traffic sourced from a single host and destined for another host to use a different path than your dynamic IGP dictates?

Use PBR.

ROUTE Notes - More IGP Redistribution

Wed, 23 Jun 2010 00:00:00 +0000

As always, feel free to correct.

Study Notes

When a router redistributes from one routing protocol to another, where does the router get the list of routes to redistribute?

From the routing table. Only IGP A’s routes (not topology or successors) are redistributed into IGP B’s domain.

What are two methods of filtering redistributed routes?

Use a route-map in the redistribute line or a distribute-list.

Of the two methods for filtering, which one has more options?

The route-map method has more options. You can match on all sorts of stuff, including an ACL or interface, and filter based on that.

ROUTE Notes - IGP Redistribution

Tue, 22 Jun 2010 00:00:00 +0000

As always, feel free to correct.

Study Questions

When you redistribute OSPF into EIGRP, what are you really redistributing?

Routes knows via OSPF Networks of OSPF-enabled interfaces

What’s the default cost of an EIGRP route redistributed into OSPF?

What’s the default metric of an OSPF route redistributed into EIGRP?

There is none since EIGRP has all those nifty k-values that have to be processed. Routes actually won’t redistribute without them.

ROUTE Notes - OSPF Virtual Links and Frame Relay Stuff

Mon, 21 Jun 2010 00:00:00 +0000

Feel free to correct. I feel like I’m missing a big piece here, so please fill in a gap if you see one. Thanks. :)

Study Questions

How many area 0s (zero) can you have in an OSPF implementation

Just one.

If my company merges with another company, and we’re both running OSPF, how can we get our networks routing together properly?

The easiest thing to do is to connect your two area 0s together through some physical link. If you can, you can use virtual links to connect an ABR to another ABR to extend the zones together.

ROUTE Notes - OSPF Filtering and Summarization

Sun, 20 Jun 2010 00:00:00 +0000

Feel free to correct all this stuff. Additions are also welcome.

Study Questions

How do I keep an area route from reaching a router in that area?

You don’t. That defeats the whole purpose of having the topology database on every router. If you filtered one route from a router, there’s no way that SPF could calculate routes correctly.

Fine, then. Where do I filter routes?

You filter routes on an ABR or ASBR. Since routers only have the whole topology for their area, it’s safe to filter routes from another area or from a redistributed routing protocol. On a more technical note, you’re filtering type-3 LSAs on an ABR and type-5 LSAs on an ASBR.

ROUTE Notes - OSPF Neighbor Relationships

Fri, 18 Jun 2010 00:00:00 +0000

Feel free to correct.

Study Questions

What are the definitions of the hello and dead intervals?

The hello intervals is how often a router sends hello messages. The dead interval is how long to wait before considering a neighbor dead from lack of hello messages; this is 4x the hello interval by default.

How do you keep OSPF from trying to detect neighbors on an interface?

Don’t configure a network statement for that interface Make that interface passive

ROUTE Notes - Controlling Routes in EIGRP

Thu, 17 Jun 2010 00:00:00 +0000

Corrections welcome.

Study Questions

Why would you ever want to summarize routes?

Summarizing routes minimizes the routes advertised to the network. For example, instead of advertising 192.168.0.0/24, 192.168.1.0/24…192.168.n.0/24, a router can advertise a single route to 192.168.0.0/16. Keeping routing tables small saves hardware resources, minimizes convergence times, helps avoid route flapping, and makes the routing table easier to read for humans.

When will an EIGRP router auto-summarize a route?

If a router has interfaces that that are in different classes of network (Class A, B, C), then that router will auto-summarize those routes up to the classful boundary. For example, if you have a 10.0.0.1/24 and a 192.168.100.1/30, the router will advertise 10.0.0.0/8 and 192.168.100.0/24.

ROUTE Notes - EIGRP Neighbor Relationships

Thu, 17 Jun 2010 00:00:00 +0000

Or neighborships, as they call it in the book. What a terrible word.

Study Questions

What settings must match between two routers in order to become EIGRP neighbors?

Both routers must be in the same primary subnet Both routers must be configured to use the same k-values Both routers must in the same AS Both routers must have the same authentication configuration (within reason) The interfaces facing each other must not be passive

ROUTE Notes - EIGRP Topology Stuff

Thu, 17 Jun 2010 00:00:00 +0000

Study Questions

How do you keep EIGRP from killing your WAN?

You can use the ip bandwidth-percent eigrp AS X command to limit the amount of bandwidth that EIGRP uses to update neighbors.

How does EIGRP calculate how much bandwidth it can use for each frame relay PVC?

By default, EIGRP takes 50% of the (sub)interface’s configured bandwidth (with the bandwidth command) to use for updates on NBMA (non-broadcast mutliaccess) networks like frame relay. This value is divided equally among all the PVC configured on that interface.

ROUTE - Redistribution Nuance #2 - OSPF External Metric Types

Sun, 06 Jun 2010 00:00:00 +0000

Last time, we talked about a nifty little lab I set up for redistribution and how the OSPF ASBRs acted a little differently than I expected. This time, let’s look at how changing external OSPF routes to a metric-type of 1 (E1) affects the routing tables.

Here’s the network again.

The static routes are being redistributed into their respective IGPs, and EIGRP is being redistributed into OSPF. Let’s look at the routing table on R1.

ROUTE - Redistribution Nuance #1 - Admin Distance FTW

Mon, 24 May 2010 00:00:00 +0000

I just got back from Global Knowledge’s ROUTE class, and I must say that it was a great class. John Barnes puts on quite the show and is the best instructor I’ve ever had. I digress, though.

One of the topics we covered was route redistribution, so I went back to the hotel one night and fired off this network in GNS3 to study a bit.

The object was to see how redistributing statics into OSPF and into EIGRP differ. It was also an opportunity to see how EIGRP redistributes into OSPF (and OSPF into EIGRP, but I didn’t make it that far). To do that, I redistributed 10.10.10.0/24 from R1 into OSPF and 10.10.20.0/24 from R4 into EIGRP. I then had R2 and R5 redistribute all EIGRP routes into OSPF. It’s a nice mix, but I saw some weirdness in the paths to 10.10.20.0/24.