MC7455: Linux Routing - Manually Configure Networking

[JM]

Silly routing question....   :)

I just got a Sierra Wireless MC7455 today, and plugged it into my linux machine running ArchLinux (4.12.4).  I installed qmicli (1.18.0) and was able to connect to Verizon.
First, this is how Arch is naming the interfaces for "/dev/cdc-wdm1" and "/dev/cdc-wdm2":

6: wwp25s0u2u7i8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 1a:22:c6:af:bf:43 brd ff:ff:ff:ff:ff:ff
7: wwp25s0u2u7i10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 0e:99:f4:4c:78:f8 brd ff:ff:ff:ff:ff:ff

Second, my connection details:
# qmicli -d /dev/cdc-wdm1 --wds-get-current-settings

[/dev/cdc-wdm1] Current settings retrieved:
           IP Family: IPv4
        IPv4 address: 100.115.2.193
    IPv4 subnet mask: 255.255.255.252
IPv4 gateway address: 100.115.2.194
    IPv4 primary DNS: 198.224.172.135
  IPv4 secondary DNS: 198.224.175.135
                 MTU: 1428
             Domains: none
Third, both interfaces are in "raw-ip" mode (this is how the MC7455 came):
# qmicli -d /dev/cdc-wdm1 --wda-get-data-format
[/dev/cdc-wdm1] Successfully got data format
                   QoS flow header: no
               Link layer protocol: 'raw-ip'
  Uplink data aggregation protocol: 'disabled'
Downlink data aggregation protocol: 'disabled'
                     NDP signature: '0'
  Uplink data aggregation max size: '0'
Downlink data aggregation max size: '0'
# qmicli -d /dev/cdc-wdm2 --wda-get-data-format
[/dev/cdc-wdm2] Successfully got data format
                   QoS flow header: no
               Link layer protocol: 'raw-ip'
  Uplink data aggregation protocol: 'disabled'
Downlink data aggregation protocol: 'disabled'
                     NDP signature: '0'
  Uplink data aggregation max size: '0'
Downlink data aggregation max size: '0'

Since the modem is in 'raw-ip' mode, I understand that dhclient / dhcpd won't work, so I need to manually configure networking.  I tried the following, which was accepted:

# ip addr add 100.115.2.193 dev wwp25s0u2u7i8
# ip route add default dev wwp25s0u2u7i8
If I try to "ping 8.8.8.8" with the above,then my machine is trying to ARP over the raw-ip interface:

    1 0.000000000 1a:22:c6:af:bf:43 → Broadcast    ARP 42 Who has 8.8.8.8? Tell 100.115.2.193
    2 1.021524595 1a:22:c6:af:bf:43 → Broadcast    ARP 42 Who has 8.8.8.8? Tell 100.115.2.193
    3 2.034858653 1a:22:c6:af:bf:43 → Broadcast    ARP 42 Who has 8.8.8.8? Tell 100.115.2.193
    4 3.048575140 1a:22:c6:af:bf:43 → Broadcast    ARP 42 Who has 8.8.8.8? Tell 100.115.2.193
What is the correct way to configure networking?  And should I change the MTU of 1500 on wwp25s0u2u7i8 to 1428 so that it matches what qmicli is reporting, or does it not matter?

Thanks so much!

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