[aprssig] Question about APRS-IS and IS->RF igating

[Phil N6TCT]

Hi, folks.  I was just looking into the configuration and log files of our igate and was confused about something, hoping you can help.

We have a bidirectional igate, GERLCH, out in the Nevada desert.  It's running aprs4r under linux.

The problem I'm seeing is typified by the following packet exchange.  We hear a message on RF and gate it to APRS-IS:

2012-05-17 07:58:45 recv on rf0: W7DEM-6 -> APBPQ1 via [SNOW*, VIRGPK*, WIDE2*]: (=3909.20N/11944.40Wo BPQ32 Igate V 5.2.6.1 )
2012-05-17 07:58:45 gating from rf0 to is0, message: W7DEM-6 -> APBPQ1 via [SNOW*, VIRGPK*, WIDE2*]: (=3909.20N/11944.40Wo BPQ32 Igate V 5.2.6.1 )
2012-05-17 07:58:45 send on is0: W7DEM-6 -> APBPQ1 via [SNOW*, VIRGPK*, WIDE2*]: (=3909.20N/11944.40Wo BPQ32 Igate V 5.2.6.1 )

A second later, we get a message via APRS-IS which looks to be something that W7DEM-6 sent only to APRS-IS:

2012-05-17 07:58:46 message recv on is0: W7DEM-6 -> APBPQ1 via [TCPIP*, QAC, T2SOCAL]: (<IGATE,MSG_CNT=0,LOC_CNT=56)

Sadly, our igate now gates this junk out onto RF:

2012-05-17 07:58:46 gating from is0 to rf0, message: W7DEM-6 -> APBPQ1 via [TCPIP*, QAC, T2SOCAL]: (<IGATE,MSG_CNT=0,LOC_CNT=56)
2012-05-17 07:58:46 send on rf0: W7DEM-6 -> APBPQ1 via [TCPIP*, QAC, T2SOCAL]: (<IGATE,MSG_CNT=0,LOC_CNT=56)

Yuck.  This message in particular doesn't seem like it's going to do anyone any favors by sending it out over RF.

My question:  Why would our igate be getting this message from APRS-IS?  Is it because we just gated a message to APRS-IS from this station?  If so, that seems weird to me.  I.e., if I just gated a packet from him, presumably I'm in RF range of him, so why would I need or want APRS-IS to hand me a packet *from* him?  (If the packet was a message addressed to him, *that* I could see…)

Relatedly, is there any automated, algorithmic way that our igate should be able to spot this and say, nah, we don't want to gate this?

Thanks for any light you can shed on this!

73,

Phil, N6TCT
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