Hi Experts,
I am testing the MTU size that BDI can support. Please take a look at my config and test below. I configured the physical interface and BDI with MTU 9190. When I do a traceroute mpls, it shows MRU 1500 suggesting that the network interfaces (BDI) can accept packets up to 1500 bytes in size without requiring fragmentation. When I ping the neighbor including the size and df, I can send up to 6354. The neighbor device is also set with MTU 9190. Can you tell me why the traceroute says 1500 MRU but I can send up to 6543? I appreciate the response.
TEST-PE#show running-config interface BDI15
Building configuration...
Current configuration : 277 bytes
!
interface BDI15
ip address 172.22.224.182 255.255.255.252
ip mtu 9190
ip ospf network point-to-point
ip ospf 1 area 0.0.0.0
mpls traffic-eng tunnels
bfd interval 300 min_rx 300 multiplier 3
ip rsvp signalling hello bfd
TEST-PE#show running-config interface gigabitEthernet 0/0/4
Building configuration...
Current configuration : 266 bytes
!
interface GigabitEthernet0/0/4
mtu 9190
no ip address
negotiation auto
service instance 15 ethernet
encapsulation dot1q 15
rewrite ingress tag pop 1 symmetric
bridge-domain 15
!
end
TEST-PE#show ip interface BDI15
BDI15 is up, line protocol is up
Internet address is 172.22.224.182/30
Broadcast address is 255.255.255.255
Address determined by non-volatile memory
MTU is 9190 bytes
Helper address is not set
Directed broadcast forwarding is disabled
TEST-PE#traceroute mpls ipv4 172.22.239.45/32
Tracing MPLS Label Switched Path to 172.22.239.45/32, timeout is 2 seconds
Codes: '!' - success, 'Q' - request not sent, '.' - timeout,
'L' - labeled output interface, 'B' - unlabeled output interface,
'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,
'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry,
'P' - no rx intf label prot, 'p' - premature termination of LSP,
'R' - transit router, 'I' - unknown upstream index,
'l' - Label switched with FEC change, 'd' - see DDMAP for return code,
'X' - unknown return code, 'x' - return code 0
Type escape sequence to abort.
0 172.22.224.182 MRU 1500 [Labels: 393/implicit-null Exp: 0/0]
L 1 172.22.224.181 MRU 9190 [Labels: 612 Exp: 0] 44 ms
L 2 172.22.224.217 MRU 9190 [Labels: 959 Exp: 0] 14 ms
L 3 172.22.224.194 MRU 9190 [Labels: 2178 Exp: 0] 13 ms
L 4 172.22.224.141 MRU 9190 [Labels: implicit-null Exp: 0] 19 ms
! 5 172.22.224.81 14 ms
TEST-PE#ping 172.22.224.181 size 6354 df
Type escape sequence to abort.
Sending 5, 6354-byte ICMP Echos to 172.22.224.181, timeout is 2 seconds:
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/17/44 ms
TEST-PE#ping 172.22.224.181 size 6355 df
Type escape sequence to abort.
Sending 5, 6355-byte ICMP Echos to 172.22.224.181, timeout is 2 seconds:
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)
TEST-PE#!
