TCPmag.com for Cisco Internetworking Professionals Wednesday, April 16, 2014  
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Q & A

read... Video Killed the Data Stream
  Scott,

We've run into a network issue. I work for a company that has software to manage and monitor digital video cameras. We have an installation in Mexico where the network is using wireless to send video back to the main building. The municipality there doesn't want to allow us to see their network configuration since they are managing it, but I'm stumped as to what might cause this.

I'm going to try and simplify the problem instead of loading up with background info. When we ping a camera, we have consistent 4-8 ms ping times. When we look at the video, however, we have virtually no frames coming in. I can see data coming in to the server using a packet sniffer, but it must be incomplete data as the frames are not shown. The cameras are set for a constant bit rate of 1,024 kbps using MPEG-4 TCP, but the data I see varies from 400-1,000 kbps. It is clear there's something blocking the data or at least corrupting it, but my confusion comes in when we are getting good, consistent pings.

For me, it seems like I'm missing a piece of information somewhere. I don't have my CCNA yet (I'm studying now), but I believe someone can define different routes for ICMP packets than TCP packets if they wanted to. Do you have an idea of what we can check? Or maybe some extra troubleshooting tips we can do if we are able to access some of the network devices? Or maybe there's something I can see using the "tcpdump" utility on the Linux server.

-- Aaron

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read... Distance Training with IS-IS
  Scott,

I read your Q&A "The Monkey Mind of Administrative Distance." The example shows OSPF and the way to change the AD using an access list. Question is, how can you do it with IS-IS?

I've found the same command under "router isis," but it has different parameters and I can't "choose" which routes get the new AD (only the ones sourced from IP or CLNS, and not via a route-map or access list or anything like that). Can you help clarify this?

-- Shai

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read... Theory, Reality and Total T-1 Bandwidth
  Scott,

I'm new to managing WAN circuits and am a little confused. I read your Q&A "Total Bandwidth of a T-1 Redux" but it didn't address the issue clearly to me. My theory on the T1 connection is that since the transmit pair of wires is separate from the receive pair of wires, you should be able to get 1.5MB up and down at the exact same time for a total aggregate throughput of 3MB. In my network monitoring, this hasn't been the case, so I'm just looking for verification. Also, does this apply to 100MB full-duplex connections?

-- Alexander

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read... 'Area 257' De-Classified
  Scott,

I ran across a question in some training materials that made no sense to me. It had to do with OSPF and area numbers. One side of the link was area 257 and the other side had to connect but was not allowed to use the phrase "area 257." The anwer provided was "area 0.0.1.1" but this made no sense to me. Can you help?

-- James

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read... Follow That Packet!
  Scott,

I have configured a DHCP (ISC) server for one of my VLANs. DHCPDISCOVER packets from a client get to the server via a helper address on a Cisco router, and the server issues a DHCPOFFER to the client from its assigned scope. I can see the above using tcpdump. However, for some reason, the offered address gets dropped somewhere on its way back to the client.

My setup is as follows: Two DHCP servers on VLAN 1 (default). Just a couple of clients on a test VLAN which requests IP addresses via the helper address.

Any suggestions/pointers?

-- Sandip

    Read... read the answer

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