Do the LTE modems have a router advertisement daemon and DHCP/DHCPv6 servers running?

[Martin Tonusoo]

Hi.

I have a D-Link DWM-222 LTE modem with Qualcomm MDM9x25 chipset. I noticed
that for example the DHCPv4 request messages, ARP request messages, NDP
router or neighbor solicitation messages often receive a corresponding
response with sub-millisecond delay. Few examples:

DHCP request in "802-3" mode:
1 0.000000000 10.30.157.53 → 10.30.157.54 DHCP 330 DHCP Request  -
Transaction ID 0xe97113fe
2 0.001295386 10.30.157.54 → 10.30.157.53 DHCP 327 DHCP ACK      -
Transaction ID 0xe97113fe

ARP request in "802-3" mode:
1 0.000000000 d6:30:df:d4:f6:33 → ff:ff:ff:ff:ff:ff ARP 42 Who has
10.30.157.54? Tell 10.30.157.53
2 0.001582404 02:50:f3:00:00:00 → d6:30:df:d4:f6:33 ARP 42 10.30.157.54 is
at 02:50:f3:00:00:00

NDP router solicitation in "802-3" mode:
1 0.000000000 fe80::c49c:20bf:6aeb:c0d7 → ff02::2      ICMPv6 62 Router
Solicitation
2 0.000674895 fe80::acb3:8d65:f49e:7799 → fe80::c49c:20bf:6aeb:c0d7 ICMPv6
118 Router Advertisement from 00:00:00:00:00:00

NDP neighbor solicitation in "802-3" mode:
1 0.000000000 fe80::c49c:20bf:6aeb:c0d7 → ff02::1:ff32:fee ICMPv6 86
Neighbor Solicitation for fe80::49a3:161d:132:fee from d6:30:df:d4:f6:33
2 0.000979237 fe80::acb3:8d65:f49e:7799 → fe80::c49c:20bf:6aeb:c0d7 ICMPv6
86 Neighbor Advertisement fe80::49a3:161d:132:fee (rtr, sol, ovr) is at
02:50:f3:00:00:00

DHCP request in "raw-ip" mode:
1 0.000000000 10.30.157.53 → 10.30.157.54 DHCP 316 DHCP Request  -
Transaction ID 0x8e1b3222
2 0.000953774 10.30.157.54 → 10.30.157.53 DHCP 313 DHCP ACK      -
Transaction ID 0x8e1b3222

NDP router solicitation in "raw-ip" mode:
1 0.000000000 fe80::c49c:20bf:6aeb:c0d7 → ff02::2      ICMPv6 48 Router
Solicitation
2 0.000452896 fe80::6ccd:b325:1fb0:9f3c → fe80::c49c:20bf:6aeb:c0d7 ICMPv6
104 Router Advertisement from 00:00:00:00:00:00

DHCPv6 information request in "raw-ip" mode:
1 0.000000000 fe80::c49c:20bf:6aeb:c0d7 → ff02::1:2    DHCPv6 92
Information-request XID: 0xb92582 CID: 00020000ab1109f5cd231dd19362
2 0.001787539 fe80::6ccd:b325:1fb0:9f3c → fe80::c49c:20bf:6aeb:c0d7 DHCPv6
120 Reply XID: 0xb92582 CID: 00020000ab1109f5cd231dd19362

Timestamp of the second packet is the time in seconds since the first
packet was captured.

In addition, the TX/RX packets counters in the output of
"--wds-get-packet-statistics" do not increase for the packets mentioned
above. On the other hand, the packet counters do increase if I send for
example an ICMP "echo request" message to 8.8.8.8 or ICMPv6 "echo request"
message to 2001:4860:4860::8888.

How to understand this? Am I correct, that my LTE modem acts as the v4 and
v6 gateway? I would have expected that the cellular provider edge equipment
is in that role. Does this mean that the LTE modem firmware runs a Router
Advertisement daemon and DHCP and DHCPv6 servers? I yes, then what protocol
is used between the LTE modem and a cellular provider to assign for example
the ISP's DNS servers addresses for the DHCP server or IP parameters for
the LTE modem?


thanks,
Martin
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