20I have a server with a static IP address connected to a Comcast Business router (Cisco DPC3941B).
I also have a second machine directly connected to the same router. It gets assigned a NAT address 10.x.x.x.
When the second machine connects to the server (or vice versa) I get very slow performance. For example, if I do an RDP connection from the second machine to the server, the screen draw is unbearably slow. Similarly, an HTTP connection from the second machine to the server (via a browser) is noticeably slow.
However, when connecting to the server from an outside network, everything seems fine. No unusual delays or performance problems.
The exact same set up with a different router (a Motorola one) did not have this problem.
Is this a problem/limitation with this router? Why? Is it the translation over the NAT? Why is that so slow?
Or is it something about my set up? Could I have misconfigured something on the server or router?
Any suggestions for debugging/diagnosing?
EDIT 27 May 2018: Added config settings
ROUTER CONFIG Router is set to defaults/factory settings except for what Comcast did to set up the static IP address, etc. Settings as follow: Bridge Mode: Disabled WiFi: Enabled (but not used) DOCSIS Software Version: dpc3941b-v303r20421762-180419a-CMCST Model: DPC3941B Vendor: Cisco Hardware Revision: 1.0 Processor Speed: 447.28 MHz DRAM: 1048576 MB Flash: 128 MB Firewall Disable Firewall for True Static IP Subnet Only: OFF Disable Gateway Smart Packet Detection: ON Disable Ping on WAN Interface: OFF Firewall Security Level: Minimum LAN-to-WAN: Allow all WAN-to-LAN: Block IDENT (port 113) Local IP Network IP Address (IPv4): 10.1.10.1 Subnet mask: 255.255.255.0 DHCPv4 Server: Enabled DHCPv4 Lease Time: 7d:0h:0m Link Local Gateway Address (IPv6): fe80::481d:70ff:fede:dcc8 Global Gateway Address (IPv6): 2603:3024:1705:3c00:481d:70ff:fede:dcc8 Delegated prefix: 2603:3024:1705:3c00::/56 DHCPv6 Lease Time: 7d:0h:0m IPV6 DNS: 2001:558:feed::1 WAN Network Internet:Active Local time:2018-05-26 14:11:06 System Uptime: 4 days 16h: 56m: 42s WAN IP Address (IPv4): 184.108.40.206 WAN Default Gateway Address (IPv4): 220.127.116.11 WAN IP Address (IPv6): 2001:558:6045:bf:31e4:2d63:9158:8238 WAN Default Gateway Address (IPv6): fe80::201:5cff:fe65:4c46 Delegated prefix (IPv6): 2603:3024:1705:3c00::/56 Primary DNS Server (IPv4): 18.104.22.168 Secondary DNS Server (IPv4):22.214.171.124 Primary DNS Server (IPv6):2001:558:feed::1 Secondary DNS Server (IPv6):2001:558:feed::2 WAN Link Local Address (IPv6): fe80::4a1d:70ff:fede:dcc7 DHCP Client (IPv4):Enabled DHCP Client (IPv6): Enabled DHCP Lease Expire Time (IPv4): 2d:10h:53m DHCP Lease Expire Time (IPv6): 2d:17h:59m Managed Sites: Disabled Managed Services: Disabled Managed Devices: Disabled Port Forwarding: Disabled Port Triggering: Disabled True Static IP Port Management: Disable all rules and allow all inbound traffic through Remote Management: Disabled DMZ: Disabled NAT: Disable All Static Routing: None Dynamic DNS: Disabled Device Discovery: Disabled
EDIT 27 May 2018 This might be relevant: Email not delivered over local wifi, delivered all other times
Perhaps the Cisco router does not support Hairpinning? But wouldn't that result in NO connection as opposed to a slow connection?