[Freeswitch-users] How to set FS_A as a gateway of FS_B??

I have already set it in my FreeSwitch\conf\sip_profiles\external.xml: <gateways> <gateway name="FreeSwitch"> <param name="username" value="1008"/> <param name="realm" value="218.210.xxx.xxx"/> <param name="password" value="1234"/> <param name="extension" value="1008"/> <param name="proxy" value="218.210.xxx.xxx"/> <param name="expire-seconds" value="3600"/> <param name="retry-seconds" value="10"/> </gateway> </gateways> But my FS_A always return a 403 to FS_B, Where is the problem??