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I need to configure Cisco 2901 router to route between interconnect block and usable ip block. Circuit is fiber 30Mb/s I got this info from ISP provider:

IP space:

Interconnect block - 50.204.xxx.80/30

Netmask: 255.255.255.248

ISP Internet gateway: 50.204.xxx.81

Customer Layer 3 device WAN interface: 50.204.xxx.82

Interconnect usable IP's: 50.204.xxx.83 thru 50.204.xxx.86

Primary DNS: x.x.x.x

Secondary DNS: x.x.x.x

Customer useable IP block - 50.204.xxx.88/29

Netmask: 255.255.255.248

Usable IPs: 50.204.xxx.89 thru 50.204.xxx.94

The /29 of usable IP space is statically routed by ISP to 50.204.xxx.82

On the Customer device connected to the ISP, ISP recommends the following:

  • Speed hardcoded to 100 Mbps* (No auto-negotiation) *Except 1G or larger circuits * Duplex hardcoded to Full (No auto-negotiation) * Traffic Shaping/Policing -- limit output rate at or below the bandwidth usage subscribed for that connection ISP is a layer 2 transport service which only allows for complete content transmission.

I was thinking about configuring this way. Please let me know if there is better way:

Setup "wan" interface (e.g gig0/0) with 50.204.xxx.82 /30. Hard code duplex and speed.

Setup "lan" interface (e.g gig 0/1) with 50.204.xxx.89 /29

Setup traffic shaping:

class-map match-any SHAPE
 match any

policy-map SHAPE
 class SHAPE
  shape average 30000000

interface GigabitEthernet0/1
 service-policy output SHAPE

Setup default route ip route 0.0.0.0 0.0.0.0 50.204.xxx.81

Also,

  1. Would it be better to setup traffic policing?

  2. Would it be better to setup traffic shaping/policing on outside interface (gig 0/0)?

  3. I am confused with ISP giving me 50.204.xxx.80/30 address for interconnect block and then saying that I can use 50.204.xxx.83 thru 50.204.xxx.86?

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1.Would it be better to setup traffic policing?

You're using shaping, which is better in this case. The important thing is to buffer your traffic before sending it to your internet provider. Consider this:

  • Your ISP asks you to set your physical interface to 100Mbps
  • Your service from the ISP is 30Mbps
  • What happens if you're already sending 30Mbps of traffic, and you need to send a ping?

By default, your Cisco 2901 router's interface will buffer based on the physical transmit rate (100Mbps) you are configuring. If you do not add traffic shaping, that ping has a decent chance of being dropped because the ISP is almost certainly policing ingress to 30Mbps on the other end. Traffic shaping allows you to buffer your instantaneous traffic in excess of 30Mbps, so it has a chance of making it past your ISP's ingress policing; otherwise your router won't even think about buffering traffic until it reaches the physical interface transmit rate (100Mbps).

Setup traffic shaping: class-map match-any SHAPE match any
policy-map SHAPE
class SHAPE
shape average 30000000
interface GigabitEthernet0/1
service-policy output SHAPE
...
Would it be better to setup traffic shaping/policing on outside interface (gig 0/0)?

You should definitely set up egress shaping on Gi0/0; consider qos, and / or wred as well.

Since Gi0/1 is a LAN-facing interface, egress shaping doesn't help much unless you need to prioritize certain traffic, or use wred on the queue (which wouldn't be a bad idea, if you set it up right).

When you configure your QoS policies, I recommend you do it in this order:

  • Test ping loss from Gi0/0 to 50.204.xxx.81 for at least 20 minutes without qos on either interface; if you don't have a clean baseline, then you'll spend a lot of time chasing the wrong packet loss in the next steps.
  • Test egress shaping rates on your Gi0/0 interface at about 200-300 byte IP packets (i.e. somewhere at or below imix sizes), and adjust the rates until you don't drop traffic to them (see below). You might need to ask them to temporarily colo some of your test equipment in their network. Failing that, you can rent a server on the internet to test with; however, that gets fairly complicated since there would likely be several additional congestion points.
  • Test egress shaping rates on your Gi0/1 interface, in the same way you did above.
  • Add wred (if you plan to do so). Test again with 3 parallel TCP streams in each traffic direction.

Test strategy:

I strongly recommend that you perform a UDP non-drop transmit rate test with whatever qos settings you choose because it's possible that your shaping rate could be slightly higher than your ISP's rate. If so, then you need to lower your shaping parameters until you don't drop traffic when you send it to them.

  1. I am confused with ISP giving me 50.204.xxx.80/30 address for interconnect block and then saying that I can use 50.204.xxx.83 thru 50.204.xxx.86?

That definitely is confusing, as far as I can tell, that sentence can be safely ignored; however, please double check with them to be sure. The reason I say this:

  • They said "ISP Internet gateway: 50.204.xxx.81"
  • They said "Customer Layer 3 device WAN interface: 50.204.xxx.82"
  • They said "The /29 of usable IP space is statically routed by ISP to 50.204.xxx.82"

Regarding your question in the comments

The routes shown in this diagram are adequate. You only need a default route to the provider, unless you plan to turn up other networks besides 50.204.xxx.88/29.

enter image description here

Side notes

  • I normally don't recommend hard-coding speed and duplex on ethernet interfaces, but this practice is entrenched in many ISP procedures, so there is no point in fighting it.
  • You should adequately protect your network with a firewall as well, as Kit suggested.
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You do not NEED to set up traffic policing but as this is a public IP, you would want to send this traffic through a firewall of some sort, normally. I would hope the ISP would gracefully adjust your utilization on their equipment rather than depending on you to handle it.

If you were going to perform traffic shaping or policing, yes, you should implement it on your /30 IP's interface.

The /30 has only two IP's available, one unusable IP for identifying the network, and one IP for identifying broadcast traffic. The ISP puts a router on their side and takes one IP. You put a layer 3 device on your side and take the second usable IP. This is standard practice.

The /29 is your usable public IP space. Since your layer 3 device is on the /30, your router does not take up one of these assignments. This is also pretty standard practice for $ISP.

  • I would not setup traffic shaping but that was one of the recommendations from ISP. I understand that /30 has only 1 ip address available for me. I am confused with them giving me /30 and then saying I can use 5 ips on that outside interface. There are 2 usable blocks 50.204.xxx.83 thru 50.204.xxx.86 and 50.204.xxx.89 thru 50.204.xxx.94. I will have firewall as separate device. – user4608 Mar 14 '14 at 20:40
  • If there is a public request for that public IP block, the ISP equipment has assigned 50.204.xxx.82 to be the (layer 3) device to direct it to. You will see it receive connection attempts for its own IP and that block. You are correct, I didn't even notice the interconnect IP block and, frankly, I don't see how you could use that with what I know about subnetting. They may have accidentally included the next empty /30 on your paperwork. – Kit Mar 15 '14 at 16:18
  • I will check with ISP Would routing work the way I set it up? Do I need to have any extra routes? Thanks – user4608 Mar 16 '14 at 16:55

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