Posts

While the concepts of QoS on vendor platforms are similar, the actual configuration is very different. I wanted to do a few posts on the differences between Junos and IOS on the normal QoS things that I do on a day to day basis. For this first post I’m going to use a very simple diagram: On the LAN are hosts with soft-phones. These phones use specific ports but do not mark packets sent with DSCP EF. Our goal here is to ensure voice packets are marked. Any UDP packet with a port number of 5060 I will mark with DSCP EF. ...

If you’re configuring an IOS router remotely with a chance of losing the device, most engineers might decide to do a reload in 5 before starting. If you happen to lose connection to the box after a change, the router will reload in 5 minutes erasing any unsaved changes. This works, but is less than ideal. It can take a few minutes for a box to reload. What happens if the box is looking after multiple customers as well? ...

A lot of people confuse the above 3 items. I’ll explain exactly what each of the 3 above items do, how you can see them, and how the routers use them to provide a L3VPN service. Let’s take the following topology for this post: Here we have 2 L3VPN customers running over our MPLS core. R5 is advertising 5.5.5.5/32. R8 is also advertising 5.5.5.5/32 Route Distinguisher The route distinguisher’s sole job is to keep a route unique while the PE routers advertise NLRI (Network Layer Reachability Information) to each other. If R5 and R8 both advertise 5.5.5.5/32 to R3, how will R3 advertise both of those routes to R4 while keeping them unique. The VPNV4 family itself doesn’t run in a VRF. It runs in the global routing instance and hence it needs something to distinguish a route. ...

A couple of interesting graphs. You can see in the following diagrams how Sandy affected the BGP table. These images I got from the CIDR report 450 AS numbers disappeared as well as roughly 3000 prefixes. Which of course gradually returned I don’t have figures for RTT to various sites as my guess is that a fair amount of trans-Atlantic traffic would’ve been quite higher. Update: RIPE has a good RTT graph over here ...

I know the title is quite a mouthful, but I did want to cover all the above in this post. Daniel asked me to check a few things as I have ready access to real switches. You learn in your studies that layer 2 control packets are ‘special’ – Special in the way that traffic going over the trunk between 2 switches does not follow the standard practice. Let’s use wireshark to see exactly what is going on in a bunch of scenarios. It’ll also give me the opportunity to do a bit of testing with SPAN and RSPAN. ...

I’ve noticed that a lot of people seem to get confused with what exactly dot1q is doing most of the time. It’s actually incredibly simply. Tagging traffic, or Trunking in Cisco-talk, is a very straightforward process. I will not be discussing ISL here as not only do I not use it, but Cisco is phasing it out on their stuff anyway. The dot1q tag is simply inserted into the layer2 header when a packet leaves a switchport over a trunk. If a frame leaves a switchport that is not a trunk, there is no dot1a tag inserted into it, regardless of what vlan the frame came from or is going to. This means that the following is a perfectly valid topology: ...

So now it’s time to actually build my topology. There are a number of issues I’d like to get my head around. It helps to know what the planned set up is going to be. I plan to use my laptop for my studies. From my laptop I’ll be connecting to my dynamips box. My dynamips box is connected to 4 switches. I need to be able to console into all 4 switches remotely, but I don’t want to buy a terminal server. I also want to be able to telnet into all the routers running on the dynamips box. ...

I’ve been busy with work and also getting my lab together so I can finally start my lab studies. I just need a couple more pieces and configuration and then I’m good to go. I’ll be using my dynamips box for the 9 routers (3725s) and 4 switches ( 2 x 3550s & 2 x 3560s) I’ll be sure to have a blog entry detailing how I’ve connected and configured everything to fit together. The dynamips box will also be my terminal server to connect to the 4 switches.

It can be quite confusing to work out what all these terms are exactly referring to. I’ll try and put a concise answer for all of them here with an example. RIB – Routing Information Base This is the route table. i.e. When you do a show ip route, the RIB is what you see AR1#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/32 is subnetted, 1 subnets C 10.255.255.5 is directly connected, Loopback0 A router may have many separate RIB’s. If you’re running vrf’s with customer, then each vrf will have a separate RIB: ...

Steve over at networking-forum.com has a contest going, and the winner can win a few sweet prizes. Take a look here: http://www.networking-forum.com/viewtopic.php?f=29&t=23223&start=0