Bonjour Jérôme,

>Pour moi mtu et ip mtu veulent dire la même chose sur un dialer (mtu ne 
>devrait pas exister car dialer n'est pas une interface physique).
mtu 1492 est automatique, je ne le configure pas moi-même c'est le routeur qui 
se rajoute cette commande.
D'ailleurs, il n'est jamais possible de supprimer ou d'augmenter la mtu d'un 
dialer ppp :

CPE(config)#int dialer 0
CPE(config-if)#mtu 1500
 MAX allowed PPPOE MTU[1492] is set as MTU
CPE(config-if)#no mtu 1492
 MAX allowed PPPOE MTU[1492] is set as MTU

>Pour voir ce que chacun dit tu peux faire un debug ppp nego pour savoir qui 
>annonce quoi en MRU (entre ton CPE, l'OLT/BNG SFR et ton LNS)
Justement c'est ici que je ne comprends pas pourquoi la MRU ne dépasse jamais 
1492 // 1464, un output :

Feb 08 07:03:16.714: PPP: Alloc Context [9713814]
Feb 08 07:03:16.714: ppp31 PPP: Phase is ESTABLISHING
Feb 08 07:03:16.714: ppp31 LCP: Event[OPEN] State[Initial to Starting]
Feb 08 07:03:16.714: ppp31 LCP: O CONFREQ [Starting] id 1 len 38
Feb 08 07:03:16.714: ppp31 LCP:    MRU 1464 (0x010405B8)
Feb 08 07:03:16.714: ppp31 LCP:    AuthProto CHAP (0x0305C22305)
Feb 08 07:03:16.714: ppp31 LCP:    MagicNumber 0x1D788BA5 (0x05061D788BA5)
Feb 08 07:03:16.714: ppp31 LCP:    MRRU 1524 (0x110405F4)
Feb 08 07:03:16.714: ppp31 LCP:    EndpointDisc 1 lns-FTTH 
(0x130F016c6e732d46545448)
Feb 08 07:03:16.714: ppp31 LCP: Event[UP] State[Starting to REQsent]
Feb 08 07:03:16.998: ppp31 LCP: I CONFREQ [REQsent] id 1 len 14
Feb 08 07:03:16.998: ppp31 LCP:    MRU 1492 (0x010405D4)
Feb 08 07:03:16.998: ppp31 LCP:    MagicNumber 0x67B01CAC (0x050667B01CAC)
Feb 08 07:03:16.998: ppp31 LCP: O CONFACK [REQsent] id 1 len 14
Feb 08 07:03:16.998: ppp31 LCP:    MRU 1492 (0x010405D4)
Feb 08 07:03:16.998: ppp31 LCP:    MagicNumber 0x67B01CAC (0x050667B01CAC)
Feb 08 07:03:16.998: ppp31 LCP: Event[Receive ConfReq+] State[REQsent to 
ACKsent]
Feb 08 07:03:16.998: ppp31 LCP: I CONFREJ [ACKsent] id 1 len 8
Feb 08 07:03:16.998: ppp31 LCP:    MRRU 1524 (0x110405F4)
Feb 08 07:03:16.998: ppp31 LCP: O CONFREQ [ACKsent] id 2 len 34
Feb 08 07:03:16.998: ppp31 LCP:    MRU 1464 (0x010405B8)
Feb 08 07:03:16.998: ppp31 LCP:    AuthProto CHAP (0x0305C22305)
Feb 08 07:03:16.998: ppp31 LCP:    MagicNumber 0x1D788BA5 (0x05061D788BA5)
Feb 08 07:03:16.998: ppp31 LCP:    EndpointDisc 1 lns-FTTH 
(0x130F016c6e732d46545448)
Feb 08 07:03:16.998: ppp31 LCP: Event[Receive ConfNak/Rej] State[ACKsent to 
ACKsent]
Feb 08 07:03:17.306: ppp31 LCP: I CONFNAK [ACKsent] id 2 len 8
Feb 08 07:03:17.306: ppp31 LCP:    MRU 1492 (0x010405D4)
Feb 08 07:03:17.306: ppp31 LCP: O CONFREQ [ACKsent] id 3 len 34
Feb 08 07:03:17.306: ppp31 LCP:    MRU 1492 (0x010405D4)
Feb 08 07:03:17.306: ppp31 LCP:    AuthProto CHAP (0x0305C22305)
Feb 08 07:03:17.306: ppp31 LCP:    MagicNumber 0x1D788BA5 (0x05061D788BA5)
Feb 08 07:03:17.306: ppp31 LCP:    EndpointDisc 1 lns-FTTH 
(0x130F016c6e732d46545448)
Feb 08 07:03:17.306: ppp31 LCP: Event[Receive ConfNak/Rej] State[ACKsent to 
ACKsent]
Feb 08 07:03:17.618: ppp31 LCP: I CONFACK [ACKsent] id 3 len 34
Feb 08 07:03:17.618: ppp31 LCP:    MRU 1492 (0x010405D4)
Feb 08 07:03:17.618: ppp31 LCP:    AuthProto CHAP (0x0305C22305)
Feb 08 07:03:17.618: ppp31 LCP:    MagicNumber 0x1D788BA5 (0x05061D788BA5)
Feb 08 07:03:17.618: ppp31 LCP:    EndpointDisc 1 lns-FTTH 
(0x130F016c6e732d46545448)
Feb 08 07:03:17.618: ppp31 LCP: Event[Receive ConfAck] State[ACKsent to Open]
Feb 08 07:03:17.646: ppp31 PPP: Phase is AUTHENTICATING, by this end
Feb 08 07:03:17.646: ppp31 CHAP: O CHALLENGE id 2 len 33 from "lns-FTTH"
Feb 08 07:03:17.646: ppp31 LCP: State is Open

>Regarde show l2tp tunnel, prend l'IP d'un OLT/BNG SFR au hasard et essaye de 
>le pinger en df pour voir si déjà tu as bien 1500 octets,
Je peux pinger une IP du BNG SFR depuis le LNS avec 1500 mais pas en 1501 (size 
150x df-bit)

Sébastien

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