|
General software and network General OS-independent software and network questions, X11, MTA, routing, etc. |
|
Thread Tools | Display Modes |
|
|||
PPPoE and MTU settings
My ISP provided ADSL modem died after a short service life and rather than purchase/rent another one, I bought a Netis Dl4201 that is soon to arrive.
I believe I have most of the config settings but am confused on the MTU. My ISP uses PPPoE which I read will not handle packets > 1492. On the FreeBSD forums, I found this advice: Quote:
I am also confused on the need for the bridge. My understanding is that bridge mode will just pass all packets to the Linksys router. My ISP's website instructions for configuring your own modem say nothing about MTU or bridge mode. Last edited by shep; 8th November 2016 at 04:20 PM. |
|
||||
PPPoE is defined by RFC 2516. Section 7 of that RFC specifies a maximum transmission unit of 1492 octets. As Ethernet uses 1500 octets, fragmentation is common.
RFC 4638 defines a mechanism designed to to exceed the 1492 octet MTU maximum. However, your Netis gateway does not mention it on its specification page. Both your ISP and your gateway would need to have support for this mechanism for you to exceed 1492 bytes. I have never used PPPoE, so I do not have any specific provisioning guidance. There is a discussion of MTU and MSS values in the pppoe(4) OpenBSD man page. Last edited by jggimi; 8th November 2016 at 05:04 PM. Reason: added pppoe(4) reference |
|
|||
Tech support at my ISP was clueless about MTU settings - a supervisor did say to set the modem's MTU to 1492 bytes. Hopefully, it was not just to make me go away.
What I'm wondering is is if I generate a data packets of 1500 octets on my system, say in an email with attachments, I would expect it to fragment when passed over the segment between the Netis modem and the ISP. My re(4) ifconfig settings show an MTU of 1500: Code:
re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 lladdr 00:e0:4d:74:59:44 index 1 priority 0 llprio 3 groups: egress media: Ethernet autoselect (100baseTX full-duplex,rxpause,txpause) status: active inet 192.168.1.3 netmask 0xffffff00 broadcast 192.168.1.255 Would it be advised to set the MTU on the LAN clients and router to 1492 bytes? Last edited by shep; 8th November 2016 at 07:23 PM. Reason: clarity |
|
|||
The pppoe(4) indicates that the issue is if I both connect via pppoe and run NAT - either one separately is not an issue. So the question is if I'm running NAT and this is also confusing. My "Learn Networking in 24 hours" handbook says that if I'm using the 192.168.1.1 address block then I am using NAT. My router does not refer to that syntax and I have disable any port forwarding or vpn.
I did set the routers MTU from Auto -> Manual at 1492. If I am running NAT then it looks like the best way to set this is via a /etc/pf.conf entry. I'm assuming they do not support jumbo frames as their supervisor instructed to set the modems mtu at 1492. Am I running NAT based on a router, dumb'd down for home users, with an address of 192.168.1.1 and a modem address of 192.168.0.1? Last edited by shep; 8th November 2016 at 11:52 PM. Reason: added dumb'd down concern |
|
|||
My network
WAN <--PPPoE-->ADSL modem 192.168.0.1 <-> router 192.168.1.1 continued: router connects to a static 192.168.1.2 printer and a static 192.168.1.3 work station vi NIC router ports. My wireless devices get dhcp address. My inclination is that I do not have NAT, I never consciously set it up but I do not want to make assumptions. |
|
||||
Your internal network is behind a NAT router: your Netis device. But your own network does not *also* use NAT. It is a single subnet.
FYI, you and millions of others have a private network in the 192.168 address range. All must use a NAT router in order to reach the Internet. Last edited by jggimi; 9th November 2016 at 03:00 AM. Reason: typos |
|
|||
I'm less confused. My Netis modem/router is a single "machine" with both pppoe and NAT. My "machines" on my private LAN do connect to the Netis pppoe+NAT.
The relevant portion from the pppoe man page Quote:
|
|
||||
And I misread your LAN configuration. You have an inner router with two NICs. One on the 192.168.0 network, the other on the 192.168.1 network. You may use NAT, but it would depend on that inner router configuration.
However the warning in the driver man page is for a router that is also connected via pppoe. |
|
|||
And I may have diagrammed my router settings incorrectly.
Under the main setup tap of the router I have entered a Local IP:192.168.1.1 and subnet mask:255.255.255.0 Under the Status Tab I have an assigned address via dhcp Quote:
What I read on bridges last night was that they would treat the modem and the router's internet rj-45 as a single network. Bridges were described as inefficient because all broadcast traffic was sent to all devices but If the router interface is the only device, that may be minimal. My needs are pretty basic and my inclination is configure for correctness, security and simplicity. |
|
||||
I don't understand the 10.0.0.2 address definition you show. But I don't think its important as you state you are using DHCP so an IP address will be assigned by your gateway router.
You are using something as an inner router, if your diagram is still sufficiently accurate. Perhaps you are using a commercial router, or perhaps this is a general purpose computer with two NICs. --- As you've learned, a bridge logically connects two (or more) networks into a single logical network, As discussed earlier in this thread, a router ... well... routes (or forwards) packets between two (or more) networks. According to the Netis documentation readily and publicly available to me -- web site, data sheet, quick installation guide -- your device does not state it can operate as a bridge. That doesn't mean it won't, just that the documentation I've seen doesn't state this. --- Setting all of that aside, let us look at configurations for an inner network, using an "inner" router such as you likely have. An inner router defines two local networks: 1) a network between the gateway modem and the router, and 2) a network between the router and all of your local devices. That outer network might just consist of a single Ethernet cable. [outer router / ISP gateway] - {net 1} - [inner router] - {net 2} - [devices...] If the inner router is configured to use NAT, then the outer router only sees a single inner device - the inner router. All of the devices on network 2 have NAT applied to their packets, and appear to all share the same IP address -- whatever the outer router has assigned to your inner router. I believe you are using NAT on an inner router, but are unaware of it, because otherwise you would have to add a route to the inner network on your outer router Here's why: If the inner router is not using NAT, the outer router needs to have a route added to its routing table, so it can route packets destined for the inner network to the inner router. If your inner router happens to be a general purpose computer running OpenBSD, NAT is defined by a "nat-to" clause added to a PF filter rule, as described in the NAT section of the PF User's Guide. If its a different OS or a commercial router, you'll have to refer to the appropriate documentation for that OS or that equipment. --- A brief introduction to routing tables: TCP/IP is a routed protocol, so that traffic can span multiple networks. Any time there is a packet to be sent to a device on another network, the sending computer inspects in its routing table. Usually, there is only one router on any network, and so there is only a single, default route for all packets destined for other networks. These default routes point at the local router's IP address. In the case of a tiered network topology -- without NAT -- as described above in this post, the outer router would require two routes in its route table: 1) a route to the innermost network, with a "next hop" pointing to the inner router, and 2) a default route, pointing outward to a router in your ISP's network. Last edited by jggimi; 9th November 2016 at 05:45 PM. Reason: typos |
|
|||
Quote:
http://www.pcwintech.com/screenshots...nksys-firmware This customer review seems to be from someone with networking knowledge: Quote:
Last edited by shep; 9th November 2016 at 06:07 PM. Reason: Added linksys |
|
||||
Thank you.
Your diagram was inaccurate, but it isn't critical. If it helps, your Linksys router is a small office / home office ("SOHO") NAT router. NAT is enabled by default, and there doesn't seem to be a mechanism to disable NAT according to the manual, or to internet searching. |
|
|||
Was the inaccuracy the router IP or lack of the 192,168.1.1 -NAT-> 10.0.0.2?
Anyway, the system dual boots Debian Testing and OpenBSD 6.0 and I've set the re0 interface to have MTU=1492 in both. The router arrives this afternoon, so I'll set it up and get familiar with the settings. Another issue came up (download speeds in OpenBSD are about 1/2 the Debian speed). That will have to wait for another thread. Thanks |
|
|||
It took the better part of the day but I'm up and running. The Netis DL4201 was a mixed bag. It provisioned OK with PPPoE but when I went to add the router I had difficulties with the router's DHCP setting provided by the modem. It was not getting a gateway.
It was much easier to set the modem using the bridge instructions and provision PPPoE at the level of the router. I set the devices in each segment with MTU of 1492 but did not test to see if the MTU setting made a difference. I'm seeing the best upload/download speeds I've had since I started the service with a cisco 678 modem. The Netis is also running cool with a 5V/800milliamp transformer. The documentation is dumd'd down and the configuration interface is buggy - I would get a javascript message that the code was corrupted when attempting to change the modem's IP 192.168.1.1 -> 192.168.0.1. Still with modem rental fees of $5/month, if it lasts more than 6 months it will pay for itself. Buying a modem from my ISP is a minimum of $90 and the word on the street is that most do not last more than 2 years. Last edited by shep; 11th November 2016 at 06:52 PM. Reason: spelling/punctuation |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
XXXterm settings questions | sepuku | OpenBSD Packages and Ports | 12 | 29th August 2011 04:44 PM |
/etc/ppp settings for Earthlink | shep | OpenBSD General | 3 | 24th December 2009 04:17 AM |
please help me understand wpa settings | gosha | OpenBSD General | 1 | 14th July 2009 11:37 AM |
Network settings | guitarscn | OpenBSD General | 13 | 18th February 2009 01:45 AM |
Modem PPPoE vs OpenBSD PPPoE | ryoken | OpenBSD Security | 13 | 15th June 2008 10:07 PM |