BR fails to send RA

[pptz]

I am facing a rather odd issue with an OT border router implementation of my own making on an ESP32 platform. According to the logs, the BR advertises its NAT64 prefix on the WiFi LAN as it should, but I don't observe the RA in a sniffer and am not able to reach end devices connected to the BR over ipv6. A reference implementation of an ESP32 BR works as expected while producing virtually the same logs. Here is a comparison of the logs between my device and the example BR (https://github.com/espressif/esp-idf/tree/master/examples/openthread/ot_br).

1. Reference:

> ipaddr

fd00:db8:a0:0:0:ff:fe00:fc10
fd0c:d918:2dce:1:d73b:a341:507d:4b1d
fd00:db8:a0:0:0:ff:fe00:fc00
fd00:db8:a0:0:0:ff:fe00:d000
fd00:db8:a0:0:84d:8ac9:1aaf:eeb1
fe80:0:0:0:b050:9:4184:f76b
Done

> br nat64prefix

Local: fd0c:d918:2dce:2:0:0::/96
Favored: fd0c:d918:2dce:2:0:0::/96 prf:low
Done

I(204194) OPENTHREAD:[I] RoutingManager: Preparing RA
I(204204) OPENTHREAD:[I] RoutingManager: - RA Header - flags - M:0 O:0
I(204204) OPENTHREAD:[I] RoutingManager: - RA Header - default route - lifetime:0
I(204214) OPENTHREAD:[I] RoutingManager: - FlagsExt - StubRouter:1
I(204234) OPENTHREAD:[I] RoutingManager: - RIO fd0c:d918:2dce:1::/64 (lifetime:1800, prf:medium)
I(204234) OPENTHREAD:[I] RoutingManager: Sent RA on infra netif 3

2. My BR:

> ipaddr

fd2f:6157:afae:1:6d1e:d858:5e2c:5bc5
fd12:d3e3:791b:bb06:0:ff:fe00:fc10
fd12:d3e3:791b:bb06:0:ff:fe00:fc00
fd12:d3e3:791b:bb06:0:ff:fe00:7c00
fd12:d3e3:791b:bb06:76f1:845b:f05c:b8e7
fe80:0:0:0:c63:703f:a83a:f0a3
Done

> br nat64prefix

Local: fd2f:6157:afae:2:0:0::/96
Favored: fd2f:6157:afae:2:0:0::/96 prf:low
Done

I(686713) OPENTHREAD:[I] RoutingManager: Preparing RA
I(686713) OPENTHREAD:[I] RoutingManager: - RA Header - flags - M:0 O:0
I(686723) OPENTHREAD:[I] RoutingManager: - RA Header - default route - lifetime:0
I(686723) OPENTHREAD:[I] RoutingManager: - FlagsExt - StubRouter:1
I(686743) OPENTHREAD:[I] RoutingManager: - PIO fd9d:e807:3acd:1dd7::/64 (valid:1800, preferred:1800)
I(686743) OPENTHREAD:[I] RoutingManager: - RIO fd2f:6157:afae:1::/64 (lifetime:1800, prf:medium)
I(686753) OPENTHREAD:[I] RoutingManager: Sent RA on infra netif 3

---

The only difference seems to be that in my implementation the RA also has a PIO option. I tried removing (that is, not adding) it programmatically for the sake of the experiment, it makes no difference.

Checking the br counters reveals that RA TxSuccess is a growing positive integer in both cases.

I'm currently digging into the underlying networking stack of the ESP device to see if there's some issue with it, but in the meanwhile thought I'd post here in case anyone might offer some additional ideas.

Thanks.

[abtink]

OT RoutingManager upon constructing the RA message will pass it to platform layer to be sent. In particular, the following otPlatInfraIf API will be invoked:

openthread/include/openthread/platform/infra_if.h

Lines 70 to 92 in 9f6921c

	/**
	* Sends an ICMPv6 Neighbor Discovery message on given infrastructure interface.
	*
	* See RFC 4861: https://tools.ietf.org/html/rfc4861.
	*
	* @param[in] aInfraIfIndex The index of the infrastructure interface this message is sent to.
	* @param[in] aDestAddress The destination address this message is sent to.
	* @param[in] aBuffer The ICMPv6 message buffer. The ICMPv6 checksum is left zero and the
	* platform should do the checksum calculate.
	* @param[in] aBufferLength The length of the message buffer.
	*
	* @note Per RFC 4861, the implementation should send the message with IPv6 link-local source address
	* of interface @p aInfraIfIndex and IP Hop Limit 255.
	*
	* @retval OT_ERROR_NONE Successfully sent the ICMPv6 message.
	* @retval OT_ERROR_FAILED Failed to send the ICMPv6 message.
	*
	*/
	otError otPlatInfraIfSendIcmp6Nd(uint32_t aInfraIfIndex,
	const otIp6Address *aDestAddress,
	const uint8_t *aBuffer,
	uint16_t aBufferLength);

May be helpful to check the implementation of this API on the platform.

[chshu]

@pptz The otPlatInfraIfSendIcmp6Nd() function is implemented and provided in the library, so the source code is not available in ESP-IDF. Do you have any specific requirement to implement the BR feature yourself, rather than using the ESP Thread BR SDK directly?

[pptz]

@pptz The otPlatInfraIfSendIcmp6Nd() function is implemented and provided in the library, so the source code is not available in ESP-IDF. Do you have any specific requirement to implement the BR feature yourself, rather than using the ESP Thread BR SDK directly?

I am using the ESP Thread BR API, as far as I can tell I'm calling the same methods as the reference ot_br ESP example, which, as I mentioned, works well. But when integrated into my product, something goes awry. I suspect that it's indeed something platform-specific, not in OT itself.

[chshu]

Could you share the steps or sample code to reproduce the issue?

[pptz]

I'll post the resolution here for the record, even though, as suspected, the problem had nothing to do with OpenThread itself.

Turned out that the LAN interface on my device did not have an IPv6 address. This logically broke route advertising on the LAN (as IPv6 routes are advertised with ICMPv6 using IPv6 addresses), but without any visible errors on the side of the Espressif port of OT.

[abtink]

Thanks for posting the resolution. 👍