MTU stands for Maximum Transmission Unit. It is a networking term that refers to the largest size of a data packet that can be transmitted in a particular network protocol.
The MTU size is important because it determines the maximum size of the data packets that can be transmitted over the network. It also may be a factor to be considered when setting up Cilium ClusterMesh.
How does MTU impact Cilium ClusterMesh?
A networking issue happened when two EKS clusters are connected with Cilium ClusterMesh that large HTTP requests or responses (> ~8.4KB) cannot be transferred across clusters.
However, all smaller HTTP requests and responses work pretty well when crossing clusters.
Tcpdump from Client
The tcpdump was taken in the client Pod with tshark:
1 0.000000 10.204.169.85 → 172.20.138.190 TCP 76 47174 → 80 [SYN] Seq=0 Win=62188 Len=0 MSS=8884 SACK_PERM TSval=2867861898 TSecr=0 WS=128
2 0.001241 172.20.138.190 → 10.204.169.85 TCP 76 80 → 47174 [SYN, ACK] Seq=0 Ack=1 Win=62104 Len=0 MSS=8884 SACK_PERM TSval=3752456813 TSecr=2867861898 WS=128
3 0.001255 10.204.169.85 → 172.20.138.190 TCP 68 47174 → 80 [ACK] Seq=1 Ack=1 Win=62208 Len=0 TSval=2867861899 TSecr=3752456813
4 0.001742…
