PSWired
join:2006-03-26
Edgewater, MD
| No ringback behind cisco NAT router
Hopefully someone here can help out with a problem I'm having.
I have a UTStarcom 2-line ATA connected to a LAN behind a Cisco 2600 router that is running NAT. Everything works fine except that I hear no ringback tone when calling out from the VOIP line. When the router is bypassed and the ATA is connected directly to the Internet I hear the ringback tone as expected.
I haven't been able to find many details through Google on how to effectively troubleshoot this. Anyone have suggestions on where to start? |
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priller
join:2000-10-20
Gainesville, VA
 ·voip.ms
·Callcentric
·Vonage
·callwithus
| Is SIP running on a port other than 5060?
If you aren't sure, do 'show ip nat translations'
If you are, then you may need to specify the port so the SIP ALG will function properly with the 'ip nat service' command.
example: ip nat service sip udp port 10000
... where the port specified is the SIP port to the provider.
The good old 'debug ip nat sip' may shed some light on the problem. |
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PSWired
join:2006-03-26
Edgewater, MD
| Thanks for the reply. SIP is indeed running on port 5060. I'm running IOS 12.3 (9a) on this system. Should I look into upgrading the IOS on this router? Bummer, would have to ruin that uptime...
Also, I am running nat overload. I'd rather not do one-to-one nat for this ATA since there may be more on the way and I don't want to gobble up public IP addresses and deal with that configuration nightmare, but do you think that could be a possible solution?
Show version:
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IK9O3S3-M), Version 12.3(9a), RELEASE SOFTWARE (f
c4)
Copyright (c) 1986-2004 by cisco Systems, Inc.
Compiled Fri 23-Jul-04 01:10 by kellythw
Image text-base: 0x80008098, data-base: 0x819E4548
ROM: System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
accessrouter uptime is 2 years, 32 weeks, 4 hours, 8 minutes
System returned to ROM by power-on
System restarted at 12:43:08 zone Mon Aug 1 2005
System image file is "flash:c2600-ik9o3s3-mz.123-9a.bin"
This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.
A summary of U.S. laws governing Cisco cryptographic products may be found at:
»www.cisco.com/wwl/export/crypto/···qrg.html
If you require further assistance please contact us by sending email to
export@cisco.com.
cisco 2611 (MPC860) processor (revision 0x202) with 61440K/4096K bytes of memory
.
Processor board ID JAB03140E4G (397792326)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
2 Ethernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)
Configuration register is 0x2102 |
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PSWired
join:2006-03-26
Edgewater, MD
| reply to PSWired
Update.
I debugged the SIP session while making an outgoing call from the ATA. It appears the ringing message is being received by the router, but apparently the SDP portion of the SIP packet has no port information, so the router pukes? Here's the log:
Mar 13 14:14:25.289: NAT: SIP: [1] processing SIP/2.0 100 Trying message
Mar 13 14:14:25.289: NAT: SIP: [1] translated embedded address 205.xxx.xxx.xxx->
172.16.20.100
Mar 13 14:14:25.289: NAT: SIP: [1] translate embedded port 1027->5060
Mar 13 14:14:29.977: NAT: SIP: [1] processing SIP/2.0 180 Ringing message
Mar 13 14:14:29.981: NAT: SIP: [1] translated embedded address 205.xxx.xxx.xxx->
172.16.20.100
Mar 13 14:14:29.981: NAT: SIP: [1] translate embedded port 1027->5060
Mar 13 14:14:29.981: NAT: SIP: [1] translated embedded address 172.16.20.100->20
5.xxx.xxx.xxx
Mar 13 14:14:29.981: NAT: SIP: [1] No port present. Use new port 5060->1027
Mar 13 14:14:29.985: NAT: SIP: [1] message body found
Mar 13 14:14:35.330: NAT: SIP: [1] processing SIP/2.0 200 OK message
Mar 13 14:14:35.330: NAT: SIP: [1] translated embedded address 205.xxx.xxx.xxx->
172.16.20.100
Mar 13 14:14:35.334: NAT: SIP: [1] translate embedded port 1027->5060
Any ideas? |
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priller
join:2000-10-20
Gainesville, VA |
Q: You don't hear ringback ... But, if the person answers you are connected normally? |
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PSWired
join:2006-03-26
Edgewater, MD | Correct, call initiates as expected. |
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tommy13v
Premium
join:2002-02-15
Glenville NY | reply to PSWired
Is SIP fixup enable on the router? |
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PSWired
join:2006-03-26
Edgewater, MD | I thought fixup was only supported on the PIX firewalls. At any rate, it's not enabled on my 2611 unless it's turned on by default. |
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PSWired
join:2006-03-26
Edgewater, MD
| reply to PSWired
I sniffed the traffic outside and inside the router while placing an outgoing call from the ATA. Outside the firewall, the following sequence occurs:
Invite
100 Trying
180 Ringing
200 OK
Inside the firewall, this happens:
Invite
100 Trying
183 Session progress
200 OK
Is the SIP ALG on the cisco mangling the ringing message? |
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Stewart
join:2005-07-13 | reply to PSWired
If your ATA will work behind a "dumb" NAT (or can be configured to do so), just turn off the ALG; IMO it only causes trouble.
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PSWired
join:2006-03-26
Edgewater, MD | Bingo!
Works fine now. Wonder what that ALG was doing to the ringing message?? |
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