linux - How to configure already statically routed IPv6 block on CentOS 7

My question is very simple yet I didn't find a solution, probably because of my lack of networking knowledge.

I have a dedicated server and I manipulate it through IPMI remotely. Recently I asked for IPv6 support from the administrator here is what I got
respond

IP Range: 2604:881:39c::/48 has been statically routed to your server.
I tried to assign an IP within this block (2604:881:39c::2) to my server then I found they didn't provide gateway address. Then I asked

Me: Can I ask what is the ipv6 gateway address?
Admin: This is a static route and does not include a gateway. All IPs are routed to your server.

I tried to configure it but I have totally no idea what the right path is. Because I don't know much about IPv6 addressing and what this "STATIC ROUTE" on upstream means here. What I have got so far is I randomly pick an address 2604:881:39c::2 and set 2604:881:39c::1 to be the gateway. Here:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no

IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=eno1
UUID=6d049769-68a1-4631-83d4-46b0f3afdf59
DEVICE=eno1
ONBOOT=yes
IPADDR=XX.XXX.XX.XX

PREFIX=30
GATEWAY=XX.XXX.XX.XX
DNS1=8.8.8.8
IPV6_PRIVACY=no
ZONE=public
DNS2=2001:4860:4860::8888
IPV6ADDR=2604:881:39c::2/48
IPV6_DEFAULTGW=2604:881:39c::1
IPV6_PEERROUTES=no

When I do tracepath6, I have:

PING ipv6.google.com(dfw28s04-in-x0e.1e100.net (2607:f8b0:4000:815::200e)) 56 data bytes
From myhostname (2604:881:39c::2) icmp_seq=1 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=2 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=3 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=4 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=5 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=6 Destination unreachable: Address unreachable

From myhostname (2604:881:39c::2) icmp_seq=7 Destination unreachable: Address unreachable
From myhostname (2604:881:39c::2) icmp_seq=8 Destination unreachable: Address unreachable

It seems like it resolved the DNS successfully but had no route to the global internet. Also, I tried ip -6 route add but it didn't work.

Does anyone have ideas about this? I am stuck.