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T1 traffic causing periodic freezes

By tjapkesg ·
Background:
We have two relatively nearby buildings, both are token-ring networks, connected via a full T1 which is split between voice and data. The T1 is linked to our networks through Andrew Bridgeports. Internet is served by a local ISP, connected via a fract T1 and comes in to a Cisco 1600, to a Watchguard firewall, then on to a Cisco 2500.

Problem:
There have been problems with large data xfers between the buildings causings all data communications to come to a screaming halt. Thelarge data transfer itself generally appears to continue, altho is normally cancelled.

This is causing problems for a contractor that is connecting to us via dialup to a local ISP, then using VPN to gain access to us through a fract T1 from theISP to us, then connects to a Citrix server in our other building on the otherside of the T1 in question. This has been a semi successful venture to replace the PCAnywhere method implemented before my employment here, and is bypassing our firewall and leaving a gaping backdoor open. Performance of the Citrix server has been excellent with exception to uptime, where it has fallen short of PCAnywhere.

I am also guessing that this has been causing our problems with our downtown office connecting to our mailserver here.

Does this sound like a basic bandwidth issue? ..or possibly a routing issue? Could it be configured in a way to limited the allowed bandwidth of any single transfer?

Could WINS be a contributing factor? We currently have a WINS server in both buildings, both with what appear to be high query failure rates. The local server receives 10 times the querries of the server downtown, which is probably a result of DHCP assigning it as the primary WINS server. I'm considering configuring the downtown clients WINS accordingly and disabling the Computer Browser server to limit WINS broadcasts. Is this worth persuing?

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T1 traffic causing periodic freezes

by ckilday In reply to T1 traffic causing period ...

I think bandwidth is part of the problem, but there are some things you can do to help you "get by" while you sort out your bandwidth needs and budget.

To help your contractor out, relocate the Citrix server to the building with the Internet connection, or move the Internet connection to the building with the Citrix server if the other servers and applications the contractor uses are located there. The idea is to place them closest to the services they need to function and not force them tocross network bottlenecks. This is a pretty standard design idea...put the services where the users are or where they enter your network. Sometimes there's a cost for duplication of servers, but you're already seeing the result of having too much traffic travel back and forth over a single link. Incidentally, a serial line is only good for about 70% of the rated bandwidth before you begin having problems.

Second, try to get a handle on what these large data transfers are, where they come from, and where they are going. If this is a specific application or batch transfer, can it be re-scheduled to take place after normal business hours, when demand for the 1/2 T is less? You will likely need some type of sniffing device/application for this.

Third, Cisco ios does support QOS (quality of service) parameters for traffic control, but you need to check out their website for the proper ios revision level and router model compatibility. It may be necessary to upgrade your ios code and possibly your router as well.
(more to come)

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T1 traffic causing periodic freezes

by ckilday In reply to T1 traffic causing period ...

For future consideration...
If your buildings are "line of sight" without any obstacles in between, consider establishing a wireless connection between the sites. Cisco's wireless division Aironet has building to building equipment that can shoot 11Mbps between buildings for about $5K. I'm not sure they support token-ring, so you may need to purchase a couple of 2600 series routers with both an ethernet and token ring interface to connect the two sites. Even with the extra cost of the routers, you can probably prove the business case in improved response time alone. Go to www.cisco.com and look for wireless solutions.

If you don't have the budget, then give serious consideration to the design of your server farm(s) and relocate servers/services as needed. This will take face time with the different departments and the programmers who support the business applications. You need to know who needs to access what, where. The application programmers can tell you how the program operates and where it might be causing problems for you.

Best wishes,
ck

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T1 traffic causing periodic freezes

by ckilday In reply to T1 traffic causing period ...

Thanks for the updated information. Sounds like your long-range plan is in place...you just need something for the next year. I'd try for a second T-1.

One more thought...Do you own the CSU/DSU's that connect to the T-1? if you can't get the money for a second line, take a look at the configuration of your CSU/DSU's and see if you can change the bandwidth allocation such that you have say 16 64K channels for data and 8 64K channels for voice instead of 12 and 12. If you lease the equipment, check with your local utility. They may be able to modify the configuration.
Best wishes,
ck

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T1 traffic causing periodic freezes

by tjapkesg In reply to T1 traffic causing period ...

Poster rated this answer

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T1 traffic causing periodic freezes

by tjapkesg In reply to T1 traffic causing period ...

I neglected to mention that restructuring our network is not an option at this point. Our downtown office is a leased office, which will be abandoned in the next year once our new building is completed. The new building will be connected via redundant fiber, thanks to it's close proximity and the fact that we own it of course.

The internet T1 comes into our main building, and the decision to Not place the Citrix server here was due to the fact that it is running proprietary software that accesses an SQL database located downtown.

It's actually this proprietary software that gives my department the most headaches, with stability issues. The app itself also runs from a server share for approx 10 local users plus the 2 citrix users. Between running the application itself and accessing the SQL server across the T1, performance was below a usable state. Duplicating the share in order to place the server in this office was considered, but support from the software vendor has been minimal. We have yet to see them incorporate support to purge old instances from the database, leaving us with a database loaded with more inactive customers than active.

I figure this is something we'll have to live with for the next year, but It'd be great to find a method to optimize things a bit. The data transfers in question have been attempts to install software onto a system in one building off of a system in the other building. We of course try to avoid this whenever possible. It seems that copying the installation files over first works out between, generally only causing lag, rather than halts.

Thanks for your advice, we will have to take a look into a few of your ideas.

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T1 traffic causing periodic freezes

by tjapkesg In reply to T1 traffic causing period ...

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