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Remote teleworkers with CME

Posted on 2010-09-22
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Last Modified: 2012-05-10
Hi,

We have a Cisco 2811 ISR running CME 7.0. We do not use it as a router, only for voice.
Is there any *safe* way to allow remote teleworkers over the WAN? e.g. SIP clients securely authenticating to CME.
I know a possible solution is using VPN, but that creates a lot of overhead and is especially problematic on mobile platforms, so I'm wondering if it's possible to open some ports to CME and have clients connect directly (similar to public SIP providers).

Thanks in advance!
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Question by:dilberty
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 33742587
Hi,

I advise to use VPN, becouse it is easy to crack the MD5 hashes of SIP!

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Accepted Solution

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Alex Bahar earned 2000 total points
ID: 33746650
You can always create an ACL to allow ports 5060 and 5061 from your teleworker IP addresses. So non-teleworker IP addresses won't be able to register CME.
You can also use GRE tunnels, which will provide a very lightweight point to point VPN tunnels. It will make your life much easier. GRE tunnels can even carry routing updates if you're planning to run dynamic routing protocols on your remote sites.
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Expert Comment

by:xReaper
ID: 33768324
>> I advise to use VPN, becouse it is easy to crack the MD5 hashes of SIP!

Yes ? heh and how do you do that with complex password ?
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Expert Comment

by:Istvan Kalmar
ID: 33768493
HI,

Please try cain for hacking sip:

http://www.oxid.it/cain.html

it is working...
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Expert Comment

by:xReaper
ID: 33769086
Looks like you have no idea what are you are talking about here, this is such time when you better say nothing if you are not sure.
Do you have any idea how hash is used ?
You can bruteforce for ages, good luck.
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Author Comment

by:dilberty
ID: 33769102
Are you sure 5060 and 5061 are sufficient? don't I need UDP ports for voice?
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Expert Comment

by:xReaper
ID: 33769237
>Are you sure 5060 and 5061 are sufficient? don't I need UDP ports for voice?

Sure, but he talks about ACL, i think what he wanted to say thay you can use ACL for 5060, and open udp ports for averyone, anywas if sip dialog do not pass there is not point to add ACL to the rtp(udp) ports for voice.
And you dont need to use 5060 5061, use only one where your cme is binded to.
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Author Comment

by:dilberty
ID: 33769350
Thanks guys. Is there any way to allow this only for specific users? Most of my users use simple passwords and besides I wouldn't want to allow them this functionality.
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Expert Comment

by:xReaper
ID: 33769375
Thats why you need ACL based on ip of your users. (external)
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Author Comment

by:dilberty
ID: 33769465
Users at home don't have a static IP address. It is assigned dynamically from the ISP, so I probably won't be able to achieve that...
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Expert Comment

by:Alex Bahar
ID: 33769480
For simplicity, you can assign an "allowed range of IP addresses/subnet" to the VOIP teleworkers. Let's call it white-list. You can then create a simple ACL that allows only that white-list ip address range access to the CME 5060 5061 ports.
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LVL 9

Expert Comment

by:Alex Bahar
ID: 33769511
Static IP addresses for home broadband cost only 2-3 dollars a month. It is worth getting it.
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Expert Comment

by:Alex Bahar
ID: 33769577
Another option is to use 2 different VPN groups which assigns IP addresses from 2 different pools> white-list and black-list IP address pools...
Thus, you can differentiate users even if they use dynamic IP addresses on their internet broadband.
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 33771565
HI,

I advise VPN.... it give more secure, and if you use g.728 or g.729 codec you able to use it without any problems! We use it over VPN...
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Expert Comment

by:Alex Bahar
ID: 33776974
IPSEC VPN is not bed of roses though. It introduces delay and bandwidth overhead.

Processing delay can be considerable if the WAN devices do not have hardware compression modules.

A single G729 voice stream over IPSEC VPN over DSL consumes about 67 kbps! Only 8kbps is the G729 payload. IPSEC VPN adds about 21kbps to a single voice stream.


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