PPPoE client MTU get trouble

longschao · August 28, 2023, 4:48am

I have a CCR1009 work in my home, and I have 2 ISP line, fiber to the home, one is called Unicom, it’s work fine, another is Telecom, it’s get a MTU trouble. Those ISP line had a lower MTU several month ago, they were 1480, but nearly, both of them changed to 1492, Unicom is automatic changed, but Telecom is not. I got a lot logs like radvd warning: invalid mtu 1492 on pppoe-out-Telecom.
I tried change /interface/pppoe-client/pppoe-out-Telecom settings, like max-mtu=1500, max-mru=1500, and /interface/ether-Telecom set mtu=1512, l2mtu=1526, and all of them not work. the interface still get value 1480 on Actual MTU mostly. maybe one in dozens time redial, I got a 1492 value of MTU.
and I tried dial Telecom with my notebook PC, OS is Windows installed, the MTU still 1480, run cmdlet ping to a public IP address can only with less than 1452 packet size. but when I was setting Telecom dial on ONU of FTTH, I got a 1492 MTU value, and Telecom line can get reply when I ping a public IP address with 1464 pack size, and I’m sure I run ping with a -f option.
I know PPPoE can not force setting up. I set CCR router loging everything try to find out what happend, I found when MTU is 1480, some LCP reply was missed:

Aug/28/2023 09:30:54 pppoe,ppp,info pppoe-out-Telecom: terminating... - administrator request
Aug/28/2023 09:30:54 pppoe,debug,packet ether5-Telecom: sent PADT to BC:99:30:ED:6A:79
Aug/28/2023 09:30:54 pppoe,debug,packet     session-id=0xf9e9
Aug/28/2023 09:30:54 pppoe,ppp,debug pppoe-out-Telecom: LCP lowerdown
Aug/28/2023 09:30:54 pppoe,ppp,debug pppoe-out-Telecom: LCP down event in initial state
Aug/28/2023 09:30:54 pppoe,ppp,info pppoe-out-Telecom: disabled
Aug/28/2023 09:30:54 pppoe,debug,packet ether5-Telecom: rcvd PADT from BC:99:30:ED:6A:79
Aug/28/2023 09:30:54 pppoe,debug,packet     session-id=0xf9e9
Aug/28/2023 09:31:06 pppoe,ppp,info pppoe-out-Telecom: initializing...
Aug/28/2023 09:31:06 pppoe,ppp,info pppoe-out-Telecom: connecting...
Aug/28/2023 09:31:06 pppoe,debug,packet ether5-Telecom: sent PADI to FF:FF:FF:FF:FF:FF
Aug/28/2023 09:31:06 pppoe,debug,packet     session-id=0x0000
Aug/28/2023 09:31:06 pppoe,debug,packet     host-uniq=0x8f0061
Aug/28/2023 09:31:06 pppoe,debug,packet     service-name=
Aug/28/2023 09:31:06 pppoe,debug,packet     ppp-max-payload=1504
Aug/28/2023 09:31:06 pppoe,debug,packet ether5-Telecom: rcvd PADO from BC:99:30:ED:6A:79
Aug/28/2023 09:31:06 pppoe,debug,packet     session-id=0x0000
Aug/28/2023 09:31:06 pppoe,debug,packet     host-uniq=0x8f0061
Aug/28/2023 09:31:06 pppoe,debug,packet     service-name=
Aug/28/2023 09:31:06 pppoe,debug,packet     ppp-max-payload=1500
Aug/28/2023 09:31:06 pppoe,debug,packet     ac-name=BJ-BJ-HJDS-MSE-1.MAN.NE40EX16
Aug/28/2023 09:31:06 pppoe,debug,packet ether5-Telecom: sent PADR to BC:99:30:ED:6A:79
Aug/28/2023 09:31:06 pppoe,debug,packet     session-id=0x0000
Aug/28/2023 09:31:06 pppoe,debug,packet     host-uniq=0x8f0062
Aug/28/2023 09:31:06 pppoe,debug,packet     service-name=
Aug/28/2023 09:31:06 pppoe,debug,packet     ppp-max-payload=1504
Aug/28/2023 09:31:06 pppoe,debug,packet ether5-Telecom: rcvd PADS from BC:99:30:ED:6A:79
Aug/28/2023 09:31:06 pppoe,debug,packet     session-id=0x64c1
Aug/28/2023 09:31:06 pppoe,debug,packet     host-uniq=0x8f0062
Aug/28/2023 09:31:06 pppoe,debug,packet     service-name=
Aug/28/2023 09:31:06 pppoe,debug,packet     ppp-max-payload=1500
Aug/28/2023 09:31:06 pppoe,ppp,debug pppoe-out-Telecom: LCP lowerup
Aug/28/2023 09:31:06 pppoe,ppp,debug pppoe-out-Telecom: LCP open
Aug/28/2023 09:31:06 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0x8e
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0x8e
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:06 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:07 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0x8f
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0x8f
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:07 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0x90
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0x90
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <mru 1500>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <magic 0xa78b892>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfReq id=0x2
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <mru 1492>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <magic 0xd7cfca86>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <auth pap>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfAck id=0x2
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <mru 1492>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <magic 0xd7cfca86>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet    <auth pap>
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: LCP opened
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent PAP AuthReq id=0x1c
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <user 01012036477>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <password 083938>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd PAP AuthAck id=0x1c
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     Authentication success,Welcome!
Aug/28/2023 09:31:08 pppoe,ppp,info pppoe-out-Telecom: authenticated
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: IPCP lowerup
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: IPCP open
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfReq id=0x37
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <addr 0.0.0.0>
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: IPV6CP open
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: MPLSCP open
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: BCP open
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: CCP lowerup
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: CCP open
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfReq id=0x1
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <addr 100.92.0.1>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfAck id=0x1
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <addr 100.92.0.1>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x0
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <magic 0xa78b892>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <data len=1484>
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPV6CP ConfReq id=0x1
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet     <interface-identifier be99:30ff:feed:6a79>
Aug/28/2023 09:31:08 pppoe,ppp,debug pppoe-out-Telecom: received unsupported protocol 0x8057
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ProtRej id=0x91
Aug/28/2023 09:31:08 pppoe,ppp,debug,packet      80 57 01 01 00 0e 01 0a be 99 30 ff fe ed 6a 79
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfNak id=0x37
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet     <addr 100.92.0.217>
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfReq id=0x38
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet     <addr 100.92.0.217>
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfAck id=0x38
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet     <addr 100.92.0.217>
Aug/28/2023 09:31:09 pppoe,ppp,debug pppoe-out-Telecom: IPCP opened
Aug/28/2023 09:31:09 pppoe,ppp,info pppoe-out-Telecom: connected
Aug/28/2023 09:31:09 pppoe,debug,packet ether5-Telecom: rcvd PADO from CC:CC:81:C1:52:12
Aug/28/2023 09:31:09 pppoe,debug,packet     session-id=0x0000
Aug/28/2023 09:31:09 pppoe,debug,packet     host-uniq=0x8f0061
Aug/28/2023 09:31:09 pppoe,debug,packet     service-name=
Aug/28/2023 09:31:09 pppoe,debug,packet     ppp-max-payload=1504
Aug/28/2023 09:31:09 pppoe,debug,packet     ac-name=BJ-BJ-DW-BAS-1.MAN.ME60-X16-KD
Aug/28/2023 09:31:09 pppoe,debug ether5-Telecom: received PADO with unknown host-uniq, dropping
Aug/28/2023 09:31:09 pppoe,ppp,debug pppoe-out-Telecom: LCP missed echo reply
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x1
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet     <magic 0xa78b892>
Aug/28/2023 09:31:09 pppoe,ppp,debug,packet     <data len=1484>
Aug/28/2023 09:31:10 pppoe,ppp,debug pppoe-out-Telecom: LCP missed echo reply
Aug/28/2023 09:31:10 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x2
Aug/28/2023 09:31:10 pppoe,ppp,debug,packet     <magic 0xa78b892>
Aug/28/2023 09:31:10 pppoe,ppp,debug,packet     <data len=1484>
Aug/28/2023 09:31:11 pppoe,ppp,debug pppoe-out-Telecom: LCP missed echo reply
Aug/28/2023 09:31:11 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x3
Aug/28/2023 09:31:11 pppoe,ppp,debug,packet     <magic 0xa78b892>
Aug/28/2023 09:31:11 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP EchoRep id=0x3
Aug/28/2023 09:31:11 pppoe,ppp,debug,packet     <magic 0xd7cfca86>

when MTU is 1492 those packet not lost:

 10:03:34 pppoe,ppp,info pppoe-out-Telecom: terminating... - administrator request
 10:03:34 pppoe,debug,packet ether5-Telecom: sent PADT to BC:99:30:ED:6A:79
 10:03:34 pppoe,debug,packet     session-id=0x44d0
 10:03:35 pppoe,ppp,debug pppoe-out-Telecom: LCP lowerdown
 10:03:35 pppoe,ppp,debug pppoe-out-Telecom: LCP down event in initial state
 10:03:35 pppoe,ppp,info pppoe-out-Telecom: disabled
 10:03:35 pppoe,debug,packet ether5-Telecom: rcvd PADT from BC:99:30:ED:6A:79
 10:03:35 pppoe,debug,packet     session-id=0x44d0
 10:03:35 system,info device changed by admin
 10:03:36 pppoe,ppp,info pppoe-out-Telecom: initializing...
 10:03:36 pppoe,ppp,info pppoe-out-Telecom: connecting...
 10:03:36 system,info device changed by admin
 10:03:36 pppoe,debug,packet ether5-Telecom: sent PADI to FF:FF:FF:FF:FF:FF
 10:03:36 pppoe,debug,packet     session-id=0x0000
 10:03:36 pppoe,debug,packet     host-uniq=0x8f0097
 10:03:36 pppoe,debug,packet     service-name=
 10:03:36 pppoe,debug,packet     ppp-max-payload=1504
 10:03:36 pppoe,debug,packet ether5-Telecom: rcvd PADO from BC:99:30:ED:6A:79
 10:03:36 pppoe,debug,packet     session-id=0x0000
 10:03:36 pppoe,debug,packet     host-uniq=0x8f0097
 10:03:36 pppoe,debug,packet     service-name=
 10:03:36 pppoe,debug,packet     ppp-max-payload=1500
 10:03:36 pppoe,debug,packet     ac-name=BJ-BJ-HJDS-MSE-1.MAN.NE40EX16
 10:03:36 pppoe,debug,packet ether5-Telecom: sent PADR to BC:99:30:ED:6A:79
 10:03:36 pppoe,debug,packet     session-id=0x0000
 10:03:36 pppoe,debug,packet     host-uniq=0x8f0098
 10:03:36 pppoe,debug,packet     service-name=
 10:03:36 pppoe,debug,packet     ppp-max-payload=1504
 10:03:36 pppoe,debug,packet ether5-Telecom: rcvd PADS from BC:99:30:ED:6A:79
 10:03:36 pppoe,debug,packet     session-id=0x6171
 10:03:36 pppoe,debug,packet     host-uniq=0x8f0098
 10:03:36 pppoe,debug,packet     service-name=
 10:03:36 pppoe,debug,packet     ppp-max-payload=1500
 10:03:36 pppoe,ppp,debug pppoe-out-Telecom: LCP lowerup
 10:03:36 pppoe,ppp,debug pppoe-out-Telecom: LCP open
 10:03:36 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
 10:03:36 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0xfd
 10:03:36 pppoe,ppp,debug,packet    <mru 1492>
 10:03:36 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:36 pppoe,ppp,debug,packet    <mrru 1500>
 10:03:36 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfRej id=0xfd
 10:03:36 pppoe,ppp,debug,packet    <mrru 1500>
 10:03:36 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0xfe
 10:03:36 pppoe,ppp,debug,packet    <mru 1492>
 10:03:36 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:36 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0xfe
 10:03:36 pppoe,ppp,debug,packet    <mru 1492>
 10:03:36 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:37 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
 10:03:37 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0xff
 10:03:37 pppoe,ppp,debug,packet    <mru 1492>
 10:03:37 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:37 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0xff
 10:03:37 pppoe,ppp,debug,packet    <mru 1492>
 10:03:37 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:39 pppoe,ppp,debug pppoe-out-Telecom: LCP timer
 10:03:39 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfReq id=0x0
 10:03:39 pppoe,ppp,debug,packet    <mru 1492>
 10:03:39 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:39 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfAck id=0x0
 10:03:39 pppoe,ppp,debug,packet    <mru 1492>
 10:03:39 pppoe,ppp,debug,packet    <magic 0x71eb46cc>
 10:03:39 pppoe,debug,packet ether5-Telecom: rcvd PADO from CC:CC:81:C1:52:12
 10:03:39 pppoe,debug,packet     session-id=0x0000
 10:03:39 pppoe,debug,packet     host-uniq=0x8f0097
 10:03:39 pppoe,debug,packet     service-name=
 10:03:39 pppoe,debug,packet     ppp-max-payload=1504
 10:03:39 pppoe,debug,packet     ac-name=BJ-BJ-DW-BAS-1.MAN.ME60-X16-KD
 10:03:39 pppoe,debug ether5-Telecom: received PADO with unknown host-uniq, dropping
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP ConfReq id=0x2
 10:03:40 pppoe,ppp,debug,packet    <mru 1492>
 10:03:40 pppoe,ppp,debug,packet    <magic 0x4aa741ca>
 10:03:40 pppoe,ppp,debug,packet    <auth pap>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP ConfAck id=0x2
 10:03:40 pppoe,ppp,debug,packet    <mru 1492>
 10:03:40 pppoe,ppp,debug,packet    <magic 0x4aa741ca>
 10:03:40 pppoe,ppp,debug,packet    <auth pap>
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: LCP opened
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent PAP AuthReq id=0x37
 10:03:40 pppoe,ppp,debug,packet     <user 01012036477>
 10:03:40 pppoe,ppp,debug,packet     <password 083938>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd PAP AuthAck id=0x37
 10:03:40 pppoe,ppp,debug,packet     Authentication success,Welcome!
 10:03:40 pppoe,ppp,info pppoe-out-Telecom: authenticated
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPCP lowerup
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPCP open
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfReq id=0x6d
 10:03:40 pppoe,ppp,debug,packet     <addr 0.0.0.0>
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPV6CP lowerup
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPV6CP open
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPV6CP ConfReq id=0x33
 10:03:40 pppoe,ppp,debug,packet     <interface-identifier 0:0:0:b>
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: MPLSCP open
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: BCP open
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: CCP lowerup
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: CCP open
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfReq id=0x1
 10:03:40 pppoe,ppp,debug,packet     <addr 100.92.0.1>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfAck id=0x1
 10:03:40 pppoe,ppp,debug,packet     <addr 100.92.0.1>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x0
 10:03:40 pppoe,ppp,debug,packet     <magic 0x71eb46cc>
 10:03:40 pppoe,ppp,debug,packet     <data len=1484>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPV6CP ConfReq id=0x1
 10:03:40 pppoe,ppp,debug,packet     <interface-identifier be99:30ff:feed:6a79>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPV6CP ConfAck id=0x1
 10:03:40 pppoe,ppp,debug,packet     <interface-identifier be99:30ff:feed:6a79>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfNak id=0x6d
 10:03:40 pppoe,ppp,debug,packet     <addr 100.92.174.166>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent IPCP ConfReq id=0x6e
 10:03:40 pppoe,ppp,debug,packet     <addr 100.92.174.166>
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPV6CP ConfAck id=0x33
 10:03:40 pppoe,ppp,debug,packet     <interface-identifier 0:0:0:b>
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPV6CP opened
 10:03:40 pppoe,ppp,info pppoe-out-Telecom: connected
 10:03:40 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd IPCP ConfAck id=0x6e
 10:03:40 pppoe,ppp,debug,packet     <addr 100.92.174.166>
 10:03:40 pppoe,ppp,debug pppoe-out-Telecom: IPCP opened
 10:03:41 pppoe,ppp,debug pppoe-out-Telecom: LCP missed echo reply
 10:03:41 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoReq id=0x1
 10:03:41 pppoe,ppp,debug,packet     <magic 0x71eb46cc>
 10:03:41 pppoe,ppp,debug,packet     <data len=1484>
 10:03:41 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP EchoRep id=0x1
 10:03:41 pppoe,ppp,debug,packet     <magic 0x4aa741ca>
 10:03:41 pppoe,ppp,debug,packet     <data len=1484>
 10:04:00 pppoe,ppp,debug,packet  pppoe-out-Telecom: rcvd LCP EchoReq id=0x1
 10:04:00 pppoe,ppp,debug,packet     <magic 0x4aa741ca>
 10:04:00 pppoe,ppp,debug,packet  pppoe-out-Telecom: sent LCP EchoRep id=0x1
 10:04:00 pppoe,ppp,debug,packet     <magic 0x71eb46cc>


[admin@MikroTik-CCR1009] /interface/pppoe-client> monitor pppoe-out-Telecom
                   ;;; B24271108
               status: connected
               uptime: 1h31m18s
         active-links: 1
             encoding: 
         service-name: 
              ac-name: BJ-BJ-HJDS-MSE-1.MAN.NE40EX16
               ac-mac: BC:99:30:ED:6A:79
                  mtu: 1492
                  mru: 1492
        local-address: 100.92.174.166
       remote-address: 100.92.0.1
   local-ipv6-address: fe80::b
  remote-ipv6-address: fe80::be99:30ff:feed:6a79

Now I need redial Telecom over 50 times eveyday for a value, or the lower MTU will cause some app in my wife’s smartphone not working.
I really need help.

longschao · August 28, 2023, 5:36am

I guess this problem maybe because Huawei devices default setting, they set PPP LCP default 3 seconds wait, but Huawei says that 3 seconds is waiting for remote peer reply. My ISP both use Huawei ME60 router for service, I don’t know why the Unicom line work fine.

mkx · August 28, 2023, 5:46am

When it comes to PPPoE, the MTU value is negotiated at session establishment between PPPoE client and server. You can set max-mtu property, but that’s only “your wish” and PPPoE server can pin it to lower value (could be it can be pinned to higher value but I’ve never seen that so far). When it comes to IPv6 MTU sizes, sent out via RAs: some ISPs have that broken (for ages), but in recent ROS versions the mismatching values get reported (as warnings) in logs. Sometimes those MTU sizes are clearly wrong (some users reported seeing values in order of 9000 on PPPoE links with MTU slightly lower than 1500), and sometimes these values seem OK (like 1492) but are still not valid.

I’ve had (mostly performance) problems with IPv6, which went away after I set /ipv6/nd/set mtu=XXXX where MTU value is actual value from PPPoE interface (obtained by running “/interface/ppppoe-client/monitor 0 once” in the line mentioning mtu). In theory this should not be required as PMTU mechanizm is required in IPv6 … but it does seem that some IPv6 routers/firewalls drop ICMPv6 messages and thus breaking PMTU process. In addition, PMTU does take some time to determine MTU and it’s beneficial to make a fixed setting which will match reality most of times. PMTU will still take place and lower the value per connection if necessary.

longschao · August 28, 2023, 6:12am

About MTU of PPPoE, yes, very ture, I know the PPPoE can not force setting up MTU. My problem is TikTok in my wife’s phone not working. I was added firewall mangle to change MSS of IPv6 lower than 1420, both direction, forward to WANs, and forward to bridge. And /IPv6/ND already set to 1480. And then I’m sure I was set accept ICMPv6 for both WAN ports.
When the Telecom line handshake MTU become 1492, TikTok will fine.

When it comes to PPPoE, the MTU value is negotiated at session establishment between PPPoE client and server. You can set max-mtu property, but that’s only “your wish” and PPPoE server can pin it to lower value (could be it can be pinned to higher value but I’ve never seen that so far). When it comes to IPv6 MTU sizes, sent out via RAs: some ISPs have that broken (for ages), but in recent ROS versions the mismatching values get reported (as warnings) in logs. Sometimes those MTU sizes are clearly wrong (some users reported seeing values in order of 9000 on PPPoE links with MTU slightly lower than 1500), and sometimes these values seem OK (like 1492) but are still not valid.

I’ve had (mostly performance) problems with IPv6, which went away after I set /ipv6/nd/set mtu=XXXX where MTU value is actual value from PPPoE interface (obtained by running “/interface/ppppoe-client/monitor 0 once” in the line mentioning mtu). In theory this should not be required as PMTU mechanizm is required in IPv6 … but it does seem that some IPv6 routers/firewalls drop ICMPv6 messages and thus breaking PMTU process. In addition, PMTU does take some time to determine MTU and it’s beneficial to make a fixed setting which will match reality most of times. PMTU will still take place and lower the value per connection if necessary.

longschao · August 28, 2023, 8:03am

I find some other forum says, some ISP set their device NOT echo reply and also NOT send echo request, in China.
OpenWRT need delete lcp-echo-interval=20, lcp-echo-failure=6 in configure, otherwise, ISP line will down and up every 2 minutes.

So I guess, I need a “disable” function for LCP

I even can’t find anything about LCP in Huawei docment.
https://support.huawei.com/enterprise/en/doc/EDOC1100092120

longschao · August 28, 2023, 8:44am

OK, I find some LCP in Huawei docments.

https://support.huawei.com/enterprise/en/doc/EDOC1100263785/6cae3eff?idPath=24030814|9856750|22715517|9858994|15969

In Configuring a VT, there is a command: ppp delay-lcp-negotiation [ force ]
I don’t know this command default value, and max delay time.
I think I hate Huawei for a little.

China Telecom and China Unicom both use Huawei ME60 router, provider their client access to the internet.

longschao · August 31, 2023, 9:27am

any one? any idea? I think I’m not the only one who get this trouble with ISP, add a “silent” or a “passive” maybe solve the problem.
I was talk to my ISP several times in nearly 3 weeks for this. and just like this LCP echo-reply, I got nothing answer about it.
https://www.linux.org/docs/man8/pppd.html

longschao · September 2, 2023, 8:47am

I was dialed my ISP line on my laptop today, it’s installed dual system, one is Ubuntu 23.04, another is Windows 11.
at first, I use Ubuntu, enabled silent option in /etc/pppd/options, and get a MTU was 1492, and I disabled silent, dial again, still 1492. it make me confuse. so I enable debug logging. got this:

2023-09-02T13:33:50.480956+08:00 longs-Inspiron-7572 pppd[5184]: Send PPPOE Discovery V1T1 PADI session 0x0 length 12
2023-09-02T13:33:50.481257+08:00 longs-Inspiron-7572 pppd[5184]:  dst ff:ff:ff:ff:ff:ff  src 8c:ec:4b:16:22:3d
2023-09-02T13:33:50.481334+08:00 longs-Inspiron-7572 pppd[5184]:  [service-name] [host-uniq  40 14 00 00]
2023-09-02T13:33:50.493282+08:00 longs-Inspiron-7572 pppd[5184]: Recv PPPOE Discovery V1T1 PADO session 0x0 length 45
2023-09-02T13:33:50.493728+08:00 longs-Inspiron-7572 pppd[5184]:  dst 8c:ec:4b:16:22:3d  src bc:99:30:ed:6a:79
2023-09-02T13:33:50.493789+08:00 longs-Inspiron-7572 pppd[5184]:  [service-name] [host-uniq  40 14 00 00] [AC-name BJ-BJ-HJDS-MSE-1.MAN.NE40EX16]
2023-09-02T13:33:50.493872+08:00 longs-Inspiron-7572 pppd[5184]: Send PPPOE Discovery V1T1 PADR session 0x0 length 12
2023-09-02T13:33:50.493936+08:00 longs-Inspiron-7572 pppd[5184]:  dst bc:99:30:ed:6a:79  src 8c:ec:4b:16:22:3d
2023-09-02T13:33:50.493995+08:00 longs-Inspiron-7572 pppd[5184]:  [service-name] [host-uniq  40 14 00 00]
2023-09-02T13:33:50.515155+08:00 longs-Inspiron-7572 pppd[5184]: Recv PPPOE Discovery V1T1 PADS session 0x7fc8 length 12
2023-09-02T13:33:50.516271+08:00 longs-Inspiron-7572 pppd[5184]:  dst 8c:ec:4b:16:22:3d  src bc:99:30:ed:6a:79
2023-09-02T13:33:50.516455+08:00 longs-Inspiron-7572 pppd[5184]:  [service-name] [host-uniq  40 14 00 00]
2023-09-02T13:33:50.516691+08:00 longs-Inspiron-7572 pppd[5184]: PADS: Service-Name: ''
2023-09-02T13:33:50.529799+08:00 longs-Inspiron-7572 pppd[5184]: using channel 2
2023-09-02T13:33:50.531818+08:00 longs-Inspiron-7572 pppd[5184]: sent [LCP ConfReq id=0x1 <mru 1492> <magic 0x599333a8>]
2023-09-02T13:33:50.549113+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [LCP ConfAck id=0x1 <mru 1492> <magic 0x599333a8>]
2023-09-02T13:33:53.448536+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [LCP ConfReq id=0x2 <mru 1492> <auth pap> <magic 0xcef205f6>]
2023-09-02T13:33:53.449903+08:00 longs-Inspiron-7572 pppd[5184]: sent [LCP ConfAck id=0x2 <mru 1492> <auth pap> <magic 0xcef205f6>]
2023-09-02T13:33:53.450539+08:00 longs-Inspiron-7572 pppd[5184]: sent [LCP EchoReq id=0x0 magic=0x599333a8]
2023-09-02T13:33:53.455996+08:00 longs-Inspiron-7572 pppd[5184]: sent [PAP AuthReq id=0x1 user="01012036477" password="083938"]
2023-09-02T13:33:53.456867+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [LCP EchoRep id=0x0 magic=0xcef205f6]
2023-09-02T13:33:53.485600+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [PAP AuthAck id=0x1 "Authentication success,Welcome!"]
2023-09-02T13:33:53.488094+08:00 longs-Inspiron-7572 pppd[5184]: sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
2023-09-02T13:33:53.488225+08:00 longs-Inspiron-7572 pppd[5184]: sent [IPV6CP ConfReq id=0x1 <addr fe80::ad5a:d9f7:db9a:9c66>]
2023-09-02T13:33:53.488351+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [IPCP ConfReq id=0x1 <addr 100.92.0.1>]
2023-09-02T13:33:53.488533+08:00 longs-Inspiron-7572 pppd[5184]: sent [IPCP ConfAck id=0x1 <addr 100.92.0.1>]
2023-09-02T13:33:53.488672+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [IPV6CP ConfReq id=0x1 <addr fe80::be99:30ff:feed:6a79>]
2023-09-02T13:33:53.488937+08:00 longs-Inspiron-7572 pppd[5184]: sent [IPV6CP ConfAck id=0x1 <addr fe80::be99:30ff:feed:6a79>]
2023-09-02T13:33:53.499086+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [IPCP ConfNak id=0x1 <addr 100.92.4.172> <ms-dns1 219.141.136.10> <ms-dns2 219.141.140.10>]
2023-09-02T13:33:53.500358+08:00 longs-Inspiron-7572 pppd[5184]: sent [IPCP ConfReq id=0x2 <addr 100.92.4.172> <ms-dns1 219.141.136.10> <ms-dns2 219.141.140.10>]
2023-09-02T13:33:53.500695+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [IPV6CP ConfAck id=0x1 <addr fe80::ad5a:d9f7:db9a:9c66>]
2023-09-02T13:33:53.513658+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ipv6-up started (pid 5212)
2023-09-02T13:33:53.514007+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [IPCP ConfAck id=0x2 <addr 100.92.4.172> <ms-dns1 219.141.136.10> <ms-dns2 219.141.140.10>]
2023-09-02T13:33:53.517713+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-pre-up started (pid 5213)
2023-09-02T13:33:53.527817+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-pre-up finished (pid 5213), status = 0x0
2023-09-02T13:33:53.530188+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-up started (pid 5218)
2023-09-02T13:33:53.530286+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ipv6-up finished (pid 5212), status = 0x0
2023-09-02T13:33:53.537144+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-up finished (pid 5218), status = 0x0
2023-09-02T13:34:36.221168+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-down started (pid 5287)
2023-09-02T13:34:36.223091+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ipv6-down started (pid 5292)
2023-09-02T13:34:36.223356+08:00 longs-Inspiron-7572 pppd[5184]: sent [LCP TermReq id=0x2 "User request"]
2023-09-02T13:34:36.223862+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ipv6-down finished (pid 5292), status = 0x0
2023-09-02T13:34:36.224117+08:00 longs-Inspiron-7572 pppd[5184]: Script /etc/ppp/ip-down finished (pid 5287), status = 0x0
2023-09-02T13:34:36.224392+08:00 longs-Inspiron-7572 pppd[5184]: rcvd [LCP TermAck id=0x2]

it seems didn’t have anything about LCP echo-request or echo-reply…

and I was try dial in windows, it got 1480 of MTU, but I don’t find a way get some log…

Flannels · March 10, 2025, 5:56am

Hey guys, this might be of use to you:
http://forum.mikrotik.com/t/pppoe-compatibility-issues-with-vbras-nfv/182546/1