rac lac lookups

PS RAC/LAC Lookups

Dave Stokes

3G SGSN config > RAN Association

Once logged in to the pageTake a note of the LAC and RAC

Numbers in decimalFor this example 58 and 58

Convert the Dec values into Hex

• Using you calculator convert the decimal values into Hex RAC=58 and LAC=58

• 58 = 3A in Hex and obviously this is the same for the LAC also but they are not always the same value so check.

• The SGSN needs 4 digits though to carryout the lookup so it becomes 003A

• Ensure you add 0’s and NOT O’s !!!!!

Create the nslookup

• The last thing to do before you type the nslookup into the SGSN is ensure you are using the correct syntax.

• The SGSN checks a different db file in the DNS for RAC/LAC lookups so the syntax for the lookup needs to change

• Nslookup racxxxx.lacxxxx.mnc0014.mcc00EA.gprs.

• So our example becomes rac003A.lac003A.mnc0014.mnc00EA.gprs.

From the above text we can see the DNS the SGSN polled (217.171.140.29 = BM-Gn1) And also the answer that was returned 217.171.141.116.

So now all we have to do is find out the SGSN with this address ??

Loopback address

• Unfortunately from the previous slide there is no quick check to determine the SGSN with this IP address it’s a matter of looking.

• First you need to know where to look though and you need to realise that the address is the loopback address of the SMM card that hosts that RAC/LAC not the loopback address of the SGSN itself !

• Basically though 217.171 is common to them all and 140 is HH, 141 is BM and 142 is MR. The last bit you need to find yourself

You need to login to the SGSN and go to Configuration > Line Cards > Choose either SMM card so either slot 1 or 10The Interfaces and you get the page above.

You’ll see in the loopback address’s the IP address we are looking for.