Orbi RBR20 v2.5.1.16 IPv6 PPPoE missing TCPMSS

[Retired_Member]

Orbi RBR20 firmware v2.5.1.16

WAN PPPoE IPv4+IPv6 - VDSL Provider - LiveTIM - Sao Paulo - Brazil

IPv4, IPv6 and IPv6-PD (LAN) are aquired as expected

I have no throuble in IPv4 services, everything works well, but many IPv6 portals fail.

I used the https://orbilogin.net/debug.htm  to capture packets and enable telnet service, also used an ODROID N2  (1 built-in and 1 usb ethernet) running ArchLinux ARM where I had lots of tools to throubleshooting support.

Results
I discovered that Orbi OS (based on OpenWrt Chaos Calmer) does not implement a simple ip6tables rule, responseble for IPv6 packet size adjust during a connection negotiation, what sometimes terminate in timeouts others in resets.

Workaround

Each time the PPPoE is established (not only after reboots), log into Orbi OS by using telnet and add the missing ip6tables rule:

ip6tables -A POSTROUTING -o ppp0 -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

Question

As I discovered this issue days after my 90 days support finished, I'm unable to report this bug through an official channel. How could I persist this soluction?

[CrimpOn · Accepted solution]

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@Retired_Member wrote:

Question

As I discovered this issue days after my 90 days support finished, I'm unable to report this bug through an official channel. How could I persist this soluction?

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What seems to have worked in this situation is to send a private message to one of the forum moderators by clicking on their screen name, such as @Dustin_V (the moderators have a capital "N" after their name).  Moderators seem to have a mechanism to communicate with Netgear engineers and support staff.

[CrimpOn · Accepted solution]

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@Retired_Member wrote:

Question

As I discovered this issue days after my 90 days support finished, I'm unable to report this bug through an official channel. How could I persist this soluction?

---

What seems to have worked in this situation is to send a private message to one of the forum moderators by clicking on their screen name, such as @Dustin_V (the moderators have a capital "N" after their name).  Moderators seem to have a mechanism to communicate with Netgear engineers and support staff.

[Retired_Member]

Let me register, the right comnand is

ip6tables -t mangle -I POSTROUTING -o ppp0 -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

PS: The command specified in the first post is missing mangle table.

[CrimpOn]

Please forgive my ignorance.  Does this situation affect every ISP connection type?

i.e. both PPPoE and DHCP?

[Retired_Member]

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@CrimpOn wrote:

Please forgive my ignorance.  Does this situation affect every ISP connection type?

i.e. both PPPoE and DHCP?

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[Retired_Member]

Once my ISP provides PPPoE only, I'm unable to try others

[Retired_Member]

MTU 1492, default for PPPoE, MSS adjusted to 1432 (-60 bytes)

MTU 1452, MSS adjusted to 1392 (-60 bytes)

Without ip6tables rule, MSS always is 1440, despite MTU value

[Retired_Member]

Other workaround is put radvd to advertase the WAN MTU value as IPv6 MTU to LAN, in PPPoE case, 1492. In this way LAN clients already send the mss 1432 and the router does not need ip6tables rule.

/tmp/radvd.conf
AdvLinkMTU 1492;


But, again, how to persist this?

[FURRYe38]

Please contact NG support or a forum moderator. 

@Blanca_O 

Thank you. 

[Retired_Member]

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@FURRYe38 wrote:

Please contact NG support or a forum moderator. 

@Blanca_O 

Thank you. 

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@FURRYe38  Thanks for your tip.

I changed the function radvd_write_config() on /etc/net6conf/6service and added instructions to use the PPPoE MTU as IPv6 MTU on /tmp/radvd.conf. Now I'm going ask @Blanca_O to help me to foward the issue to NG support, once my 90 days support has expired.

        if [ "x$w6_type" = "xpppoe" ]; then   
                local IPV6_MTU=$($CONFIG get wan_pppoe_mtu)
                printf '\tAdvLinkMTU %s;\n' "$IPV6_MTU"    
        fi

...
radvd_write_config() {
        local DHCPS_ENABLE=$1
        local PREFIX=$2
        local PRELEN=$3
        local VALID_TIME=$4
        local PREFER_TIME=$5
        local DNS=$6
        local IPV6_ADDR
        local PD_INFO
        local OLD_PREFIX
        local OLD_PRELEN
        local OLD_PD_INFO

        printf 'interface %s {\n' "$bridge"
        printf '\tAdvSendAdvert on;\n'
        printf '\tAdvCurHopLimit 64;\n'
        printf '\tMinRtrAdvInterval 198;\n'
        printf '\tMaxRtrAdvInterval 600;\n'
        printf '\tAdvDefaultLifetime 1800;\n'
        printf '\tAdvReachableTime 0;\n'
        printf '\tAdvRetransTimer 0;\n'
        printf '\tAdvDefaultPreference low;\n'
        printf '\tAdvHomeAgentFlag off;\n'
        if [ "x$w6_type" = "xpppoe" ]; then   
                local IPV6_MTU=$($CONFIG get wan_pppoe_mtu)
                printf '\tAdvLinkMTU %s;\n' "$IPV6_MTU"    
        fi                                                 
        if [ "$DHCPS_ENABLE" = "0" ]; then
                printf '\tAdvOtherConfigFlag on;\n'
                printf '\tAdvManagedFlag off;\n'
...