What causes "send_request except:%r" in XX-net/XX-Net?

Check the configured DNS server IPs are valid and reachable for the socket family used (verify with check_ip_valid4 routing in the code)

XX-net/XX-Net · warning

send_request except:%r

Error message

send_request except:%r

What it means

send_request() failed to send a UDP DNS query packet to the upstream server. This is a socket sendto() failure — typically ICMP port unreachable, network unreachable, invalid address family, or the socket not being connected/bound. The query is dropped and the caller's waiter eventually times out.

Source

Thrown at code/default/smart_router/local/dns_query.py:270

                    que.put(ips)
            except Exception as e:
                xlog.exception("dns recv_worker except:%r", e)

        xlog.info("DNS Client recv worker exit.")
        sock.close()

    def send_request(self, id, server_ip, domain, dns_type):
        try:
            d = DNSRecord(DNSHeader(id))
            d.add_question(DNSQuestion(domain, dns_type))
            req4_pack = d.pack()

            if utils.check_ip_valid4(server_ip):
                self.sock.sendto(req4_pack, (server_ip, 53))
            else:
                self.sock6.sendto(req4_pack, (server_ip, 53))
        except Exception as e:
            xlog.warn("send_request except:%r", e)

    def query_by_system(self, domain, dns_type):
        ips = []
        try:
            t0 = time.time()
            ip = socket.gethostbyname(domain)
            t1 = time.time()
            ips.append(ip)

            xlog.debug("query_by_system, %s %d cost:%f, return:%s", domain, dns_type, t1 - t0, ips)
        except Exception as e:
            xlog.warn("query_by_system %s %d e:%r", domain, dns_type, e)

        return ips

    def query(self, domain, dns_type=1, timeout=3):
        if sys.platform == "ios":
            return self.query_by_system(domain, dns_type)

View on GitHub (pinned to cfa5bc17b6)

Solutions

Check the configured DNS server IPs are valid and reachable for the socket family used (verify with check_ip_valid4 routing in the code)
Test outbound UDP 53: 'dig @8.8.8.8 example.com' from the same host
Open/allow outbound UDP 53 in the local firewall or VPN split-tunnel config
Fall back to TCP/TLS/HTTPS DNS transports (this module's TCP, DoT, DoH query classes) since port 53 UDP is commonly blocked

Defensive patterns

Strategy: fallback

Prevention

Pre-check DNS server reachability before sending: try a cheap UDP probe or keep a health flag per server
Maintain multiple upstream servers and rotate on send failure
In restrictive environments use DoH on 443 instead of UDP 53

When it happens

Trigger: sendto() to (server_ip, 53) raising because the DNS server IP is unreachable, an IPv6 address being passed to the IPv4 socket (or vice versa), the network interface being down, or a local firewall rejecting outbound UDP 53.

Common situations: Firewalled outbound port 53 (common in corporate networks forcing internal DNS), wrong IP family in the DNS config, VPN routing breaking UDP, transient network loss.

Related errors

AI-assisted analysis of XX-net/XX-Net@cfa5bc17b6 (2026-08-27). Data as JSON: /api/errors/cc36096484d8e07e. Report an issue: GitHub.