Khac phuc su co mang khong day.

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Khac phuc su co mang khong day

Khi gap phai van de ket noi may khach khong day (chang han nhu desktop, laptop, smartphone hoac e-reader) voi mang van phong, cac meo go roi ve ket noi tung buoc nay se giup ban rat nhieu dieu bo ich..

Khac phuc su co mang khong day - Ban co dau.
Khac phuc su co mang khong day - Ban khong dau.
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1. Bat dau bang cach kiem tra lai cac ket noi vat ly – Buoc thuc hien don gian nay thuong bi bo qua. Hay kiem tra lien ket tu cong WAN cua router khong day den modem bang thong rong va cac lien ket tu cac cong LAN den cac may khach Ethernet. Bao dam rang cap WAN va LAN duoc cam chat va cac den trang thai deu co tren cac dau. Neu khong:

- Thu thay the cap Ethernet de loai tru truong hop cap bi hong. 

- Kiem tra huong dan su dung cua router khong day de bao dam rang ban dang su dung dung kieu cap – mot so duong uplink cho WAN yeu cau cap dau cheo. 

- Neu cac den trang thai khong sang, ket noi mot thiet bi khac giong nhu laptop voi cong WAN hoac cong LAN bi anh huong. Neu trang thai thay doi thi dieu do co nghia thiet bi ma ban vua thay the co the bi loi trong viec tu dong dieu dinh lien ket. Kiem tra cau hinh cho cac cong tren ca hai dau va cau hinh lai sao cho phu hop toc do cong va che do duplex.


Hinh 1: Kiem tra cac ket noi vat ly

2. Tham dinh rang adapter khong day cua may khach duoc cai dat va lam viec dung cach. Tren may tinh Windows, chon ket noi khong day tu panel Network Connections va tham dinh trang thai cua no la "Enabled".

- De vao duoc Network Connections:

  • Trong Windows XP, su dung Control Panel de truy cap Network Connections.
  • Tren Windows Vista, su dung Control Panel de mo Network and Sharing Center, sau do kich Manage Network Connections.
  • Tren Windows 7, su dung Control Panel de mo Network and Sharing Center, sau do kich Manage Wireless Networks

- Neu adapter Wi-Fi o ngoai va khong xuat hien trong Network Connections, co the van de se lien quan den khe ExpressCard, khe PC Card hoac cong USB. Neu remove mot cach vat ly va ket noi lai adapter ngoai khong tro giup duoc gi, hay su dung Device Manager de uninstall/reinstall adapter do. 

- Voi bat cu kieu adapter Wi-Fi nao, neu ket noi khong duoc hien thi trong Network Connections hoac khong duoc kich hoat, hay mo panel Properties cua adapter, kich Configure, bao dam thiet bi duoc kich hoat, khong co xung dot ve tai nguyen va kiem tra cac nang cap driver neu co.


Hinh 2: Tham dinh cai dat Wi-Fi adapter cua may khach

3. Tham dinh dung cac thiet lap LAN cua router khong day. Su dung tien ich quan tri cua router de tham dinh cac dia chi IP dang gan cho cac may khach khong day.

- Neu khong biet cach truy cap vao tien ich quan tri cua router, ban hay tim trong huong dan su dung cua no. Trong da so cac truong hop, trinh duyet web se co the mo dia chi IP mac dinh duoc gan cho cong LAN cua router (cho vi du http://192.168.1.1) 

- Quan sat cac thiet lap LAN cua router. Bao dam DHCP Server cua router duoc kich hoat va duoc cau hinh de gan cac IP tu dai khong bi chong lan trong cung mot subnet voi dia chi cong LAN cua router (cho vi du nhu 192.168.1.50-100). 

- Neu DHCP Server cua router duoc cau hinh de loc truy cap khong day bang dia chi MAC, hay add dia chi MAC cua adapter Wi-Fi cua ban vao danh sach cac thiet bi duoc phep (allowed device) cua router. (De xac dinh dia chi MAC cua adapter, ban hay mo panel Network Connection/Status/Details cua may khach va tim "Physical Address"). 

- Kiem tra trang Log hoac Status cua router de tham dinh rang dia chi IP qua thuc da duoc gan cho may khach khong day bat cu khi nao no ket noi.


Hinh 3: Tham dinh cac thiet lap LAN cua router

4. Tham dinh cac thiet lap TCP/IP cua may khach. Mac du chung toi mo ta bang viec su dung Windows de quan ly cac ket noi khong day ben duoi, nhung viec khac phuc su co cung tuong tu nhu vay khi ban su dung cac chuong trinh quan ly ket noi khac (chang han nhu Intel, Linksys) hoac cac thiet bi (chang han nhu iPod, Android).

- Mo Network Connections nhu gioi thieu trong buoc 2 va kiem tra trang thai Status cua adapter. Neu Status van o che do "Disabled", hay tro ve buoc 2. Nguoc lai:

  • Tren Windows XP, neu Status la "Not Connected," su dung "View Available Networks" de tim ten mang cua rieng ban.
  • Tren Windows Vista, neu Status la "Not Connected," su dung "Connect/Disconnect" de tim ten mang cua rieng ban.
  • Tren Windows 7, neu Status la "Connections are available", tim ten mang cua rieng ban trong danh sach Wireless Network Connection ben duoi.
  • Chon ten mang cua ban va kich Connect. Neu ten mang cua ban khong duoc hien thi hoac ban khong the ket noi thanh cong, hay chuyen sang buoc 8. 

- Khi thuc hien ket noi, Status co the thay doi trong mot thoi gian ngan thanh "Acquiring Network Address", sau do chuyen thanh "Connected". Tai day, su dung Status de xac dinh dia chi IP duoc gan cua may khach. Neu IP cua may khach la 0.0.0.0 hoac 169.254.x.x, hay kich "Repair" (XP) hoac "Diagnose" (Vista/7). Neu van de van ton tai, hay chuyen sang buoc 8. 

- Nguoc lai, neu dia chi IP cua may khach da ket noi khong nam trong subnet LAN cua router, hay cau hinh ket noi de dat duoc dia chi IP tu dong va lap lai buoc 4.

 

  • Tren Windows XP, mo Properties cua adapter, chon muc co ten "Internet (TCP/IP)" va kich Properties.
  • Tren Windows Vista hoac 7, mo Properties cua adapter, chon muc co ten "Internet Protocol Version 4" va kich Properties.

 

Hinh 4.1. Tham dinh dia chi IP cua may khach (Windows XP)

Hinh 4.2. Tham dinh dia chi IP cua may khach (Windows 7)

5. Khi may khach co dia chi IP hop le ben trong subnet LAN cua router, su dung "ping" de tham dinh ket noi mang. Mo cua so Command Prompt tu menu Start cua may khach va su dung no de ping dia chi IP LAN cua router nhu the hien trong hinh 5.

- Neu hanh dong ping router cua ban lien tuc bi that bai, nhay sang buoc 6. 

- Neu hanh dong ping cua ban thanh cong, tiep tuc ping cac may khach trong LAN khong day hoac chay day khac ma ban muon chia se file hoac may in voi. Neu ping that bai, su cach ly AP co the da bi kich hoat hoac dich den co the dang su dung tuong lua de khoa luu luong gui den.

  • Kiem tra cau hinh cua router de tim ra tuy chon khong cho cac may khach khong day truyen thong voi nhau. Neu ban tim ra tham so "AP isolation", hay vo hieu hoa no.
  • Su dung Control panel cua may tinh Windows 7, Vista hoac XP de mo Windows Firewall. Neu phat hien thay tuong lua duoc kich hoat, hay tam thoi vo hieu hoa no.
  • Neu Windows Firewall khong duoc kich hoat, hay kiem tra xem co chuong trinh bao mat khac co the cung dang chay mot tuong lua ca nhan. Cho vi du, nguoi dung McAfee can mo SecurityCenter, kich "Internet & Network", va bao dam rang chuc nang bao ve tuong lua da bi vo hieu hoa.  

- Sau khi vo hieu hoa chuc nang tuong lua, ban hay thu ping lai lan nua. Neu hanh dong ping luc nay thanh cong thi tuong lua ma ban da vo hieu hoa co the cung khoa luon cac giao thuc Windows Network se duoc su dung de chia se cac file va may in. Cau hinh lai (va sau do kich hoat lai) tuong lua do de cho phep chi luu luong ma ban muon trao doi giua cac may khach trong LAN. Cho vi du, chia se cac file va may in, cho phep cac ket noi NetBIOS tu subnet LAN cua ban.


Hinh 5: Test va cho phep luu luong mong muon

6. Neu may khach cua ban van khong the ket noi, mac du da nhan dia chi IP hop le hoac da ping duoc router cua ban, thi day la thoi diem ban can tim kiem cac van de cu the khac. Router va may khach phai su dung cac chuan 802.11 tuong thich. Bang cac chuan tuong thich duoc cho ben duoi.

Client vs. Router

11b

11a

11g

11a+g

11n (single)

11n (dual)

11b

x

11a

x

x

x

11g

x

11a+g

11n (single band)

x

11n (dual band)

Cho vi du, neu ban co mot may khach 802.11a, no co the duoc ket noi voi router 802.11a, 802.11a+g, hoac 802.11n (dual band). Mac du vay, mot may khach 802.11a khong the su dung voi router 802.11b, 802.11g, hoac 802.11n (single band).

- De xac dinh xem san pham cua ban ho tro chuan nao, tim kiem cac logo nhan thuc Wi-Fi tren hop hoac trong huong dan su dung, hoac tim kiem cac san pham nhan thuc Wi-Fi tai Wi-Fi Alliance website: http://www.wi-fi.org/search_products.php. Voi cac san phan 802.11n, kich "View Wi-Fi certifications" de xac dinh su ho tro ve bang tan.

Hinh 6.1. Kiem tra kha nang tuong thich cua adapter va router Wi-Fi

Khi da xac nhan rang router va adapter may khach cua ban la tuong thich voi nhau, hay so sanh cac thiet lap khong day cua router voi cac tham so ket noi cua may khach.

- Neu cac may khach la 11b, ban phai kich hoat "b protection" tren router 11g hoac 11n cua minh (doi khi con duoc goi la Mixed Mode)

- Neu cac ket noi may khach non-11n that bai, hay bao dam rang router cua ban khong duoc thiet lap o che do hoat dong “N-only” (doi khi duoc goi la Greenfield Mode).

- Neu cac ket noi may khach 11b, 11g, va 11n (single band) that bai, bao dam rang ban khong thiet lap router 11n (dual band) o che do 5 GHz hoac 40 MHz channels.

- Neu cac ket noi may khach 11a that bai, hay bao dam ban khong thiet lap router 11n (dual band) cua minh o che do 2.4 GHz hoac 40 MHz channels.

- Neu mang cua ban co cac may khach trong ca hai bang tan, hay bao dam rang router 11n cua ban dang ho tro che do luong bang tan (dual band).

- Neu router va may khach tuong thich voi nhau nhung SSID cua router khong xuat hien trong danh sach Available Networks cua may khach, hay kich hoat "SSID broadcast".

- Mac du viec vo hieu hoa "SSID broadcast" la khong duoc khuyen khich, nhung cac WLAN co the lam viec theo cach nay neu ca may khach duoc cau hinh voi SSID cua router. Trong Windows 7, su dung Manage Wireless Networks de them vao mot Network Profile. Nhap SSID cua router vao Network Name, thiet lap cac tham so bao mat (xem buoc 7) va tich chon "Connect even if this network is not broadcasting". Can biet rang mot so may khach (dac biet mot so thiet bi dien tu dan dung) khong ho tro tuy chon nay.


Hinh 6.2: Cau hinh cac thiet lap khong day tuong thich tren router

7. Neu may khach khong day co kha nang tuong thich va router co the “nghe” duoc nhau nhung van khong the ket noi hoac trao doi luu luong, hay tim kiem loi kieu bao mat. May khach phai ho tro che do bao mat duoc yeu cau boi router: Open, WEP, WPA, hoac WPA2. Tru khi WLAN o che do Open (che do khong an toan), router va may khach phai duoc cau hinh voi cac khoa giong nhau de ma hoa luu luong giua chung. So sanh cac thiet lap bao mat WLAN cua router voi thuoc tinh ket noi khong day cua may khach va co gang khop chung.

- De xem va cau hinh cac tham so bao mat cua may khach:

 

  • Tren Windows 7, chon ten mang tu Manage Wireless Networks, mo Properties va chon tab Security.
  • Tren Windows XP, chon ket noi tu Network Connections, mo Properties, chon tab Wireless Networks, chon ten mang tu danh sach Preferred Networks va kich Properties.

 

- Neu router cua ban su dung WEP, thiet lap ma hoa cua may khach la WEP va khop kieu nhan thuc cua router (mo hoac chia se). Copy khoa WEP dau tien cua router vao may khach, dich tu dinh dang ASCII dsang hex neu can.

- Neu router cua ban su dung che do ma hoa WPA-Personal, hay thiet lap nhan thuc cho may khach la WPA-Personal (hay cung duoc biet den la WPA-PSK) va khop kieu ma hoa cua router (thuong la TKIP). Su dung mat khau cua router lam khoa mang cua may khach.

- Neu router su dung WPA2-Personal, hay thiet lap nhan thuc la WPA2-Personal (WPA2-PSK) va khop kieu ma hoa cua router (thuong la AES). Su dung mat khau cua router lam khoa mang cua may khach.

- Neu router su dung WPA hoac WPA2-Personal va ho tro Wi-Fi Protected Setup (WPS), ban co the tu dong cau hinh cac thiet lap bao mat cua may khach.

- Neu router su dung WPA hoac WPA2-Enterprise, thiet lap nhan thuc cua may khach la WPA hoac WPA2 mot cach tuong ung, khop kieu ma hoa cua router va tiep tuc cai dat 802.1X trong buoc 8.

- Neu tat ca may khach cua ban deu co the ho tro WPA2/AES, hay cau hinh router cua ban o che do WPA2/AES; cach thuc nay se cai thien duoc do bao mat va cho phep toc do 11n lon hon 54 Mbps. Mac du vay, neu ban co cac may khach WPA/TKIP-only cu, cac ket noi cua chung se that bai tru khi router cua ban duoc cau hinh de chap nhan ca WPA/TKIP va WPA2/AES.


Hinh 7: So khop cac thiet lap bao mat cua may khach va router

8. Bao dam RADIUS lam viec. WPA va WPA2-Enterprise se ghi may khach vao mang va phan phoi cac khoa ma hoa bang RADIUS server co tinh nang 802.1X. Nguoc lai, hay thuc hien theo cac buoc sau:

- Cau hinh lai router va may chu cua minh voi cong RADIUS hop le.

- Cau hinh lai RADIUS server de chap nhan cac yeu cau tu IP cua router.

- Tu router cua minh, ping IP cua RADIUS server de kiem tra kha nang reach cua mang.

- Xem bo den goi du lieu cua router de tham dinh rang RADIUS dang duoc gui.

- Su dung LAN analyzer (chang han nhu Wireshark) de capture cac luu luong duoc trao doi giua router va may chu, muc dich xem cac goi RADIUS Access-Reject.

- Tren may khach Windows, nhap "netsh ras set tracing * enabled" de ghi cac noi dung go roi 802.1X vao file Wzctrace.log.

Hinh 8: Bao dam RADIUS dang lam viec

9. Neu RADIUS lam viec nhung cac yeu cau truy cap cua may khach bi tu choi, hay chuyen sang tim kiem van de voi 802.1X Extensible Authentication Protocol (EAP) hoac dang nhap nguoi dung. May khach cua ban phai ho tro mot trong cac kieu EAP duoc yeu cau boi RADIUS server va phai cung cap mot dang nhap hop le va password/the/chung chi hoac kieu chung chi nao do. Kiem tra cac thiet lap bao mat cua may khach co lien quan voi ten mang cua ban, bat dau voi panel Security (Windows 7) hoac Authentication (Windows XP) duoc gioi thieu trong buoc 7.

- Neu may chu cua ban yeu cau EAP-TLS, hay chon "Smart Card or other Certificate" va kich "Settings" de tiep tuc.

- Neu may chu cua ban yeu cau PEAP, hay chon "Protected EAP" va kich "Settings".

- Neu may chu cua ban yeu cau EAP-TTLS, hay cai dat chuong trinh 802.1X Supplicant cua ben thu ba nao do, chang han nhu Juniper OAC hoac Cisco SSC tren may khach va thuc hien theo cac huong dan cai dat cua chuong trinh do.

- Bao dam thuoc tinh EAP cua may khach va may chu khop nhau, gom co chung chi may chu Trusted Root Authority, ten mien may chu (tuy chon), va phuong phap nhan thuc duoc tao duong ham (chang han nhu EAP-MSCHAPv2).

- Neu ban duoc nhac nho de chap nhan chung chi may chu tai thoi diem ket noi, hay kiem tra chung chi mot cach can than, tham dinh lai don vi phat hanh va su nhan dang. Khong bao gio add cac chung chi nghi ngo vao root tin cay hoac danh sach may chu cua ban.

- Neu van de EAP-TLS van ton tai, hay su dung Internet Explorer de tranh tra chung chi cua may khach va bao dam rang chung chi la hop le (chang han nhu khong bi het han).

- Neu cac van de PEAP van ton tai, su dung nut CHAP Configure de ngan chan cac dang nhap tu dong cua Windows va nhap vao username va password hop le khi duoc nhac nho.

- Neu van chua khac phuc duoc van de, can tham khao cac tai lieu 802.1X cua RADIUS server ve cau hinh EAP va nhung meo go roi. Tren Windows 7, ban co the kich nut Advanced Settings tren tab Security de cau hinh cac tuy chon giong nhu dang nhap mot lan, may tinh voi nhan thuc nguoi dung, va roaming nhanh.


Hinh 9: Tham dinh cac thiet lap 802.1X/EAP cua may khach

10. Neu may khach khong day cua ban van khong the ket noi hoac luon ket noi voi mot toc do du lieu rat thap, khi do ban co the dang bi loi kieu tham so 802.11n. De khac phuc hien tuong nay, ban co the thuc hien nhu sau:

- Neu router 802.11n (single band hoac dual band) duoc cau hinh de su dung kenh 40-MHz, hay cau hinh lai router de su dung cac kenh 20 MHz. Nhieu may khach khong ho tro cac kenh 40 MHz, dac biet la cac may khach non-11n (dual band).

- Neu router 802.11n (single band hoac dual band) duoc cau hinh de tu dong chon kenh co san trong bang tan 2.4 GHz, hay tam thoi cau hinh lai router de su dung kenh 1, 6 hoac 11 de tranh hien tuong xuyen nhieu giua cac kenh hoac thuong xuyen thay doi kenh.

- Neu router 802.11n (dual band) duoc cau hinh de su dung Dynamic Frequency Selection (DFS) trong bang tan 5 GHz, hay tam thoi cau hinh lai router de su dung kenh 36, 40, 44 hoac cac may khach 48. 11n, 11a+g va 11a ho tro cac kenh trong bang tan 5 GHz co the khac; cac kenh thap hon thuong duoc su dung nhieu hon.

- Neu router 802.11n (dual band) duoc cau hinh de su dung Band Steering va cac may khach dual band dang gap phai van de mat ket noi mot cach thuong xuyen, hay thu vo hieu hoa tuy chon do.

- Neu may khach luon ket noi o mot toc do thap hon mong doi, hay kiem tra cau hinh cua router. Toc do lon nhat cua 802.11n phu thuoc vao anten va cac tuy chon:

 

  • Router 2x2 su dung cac kenh 20 MHz co the cho toc do len den 144 Mbps (MCS 15). Router khong co Short Guard Interval (SGI) chi cho toc do dung lai o 130 Mbps.
  • Router 2x2 su dung cac kenh 40 MHz co the dat toi toc do 300 Mbps (MCS 15). Router khong SGI chi dung lai o toc do 270 Mbps.
  • Router 3x3 su dung cac kenh 40 MHz co the dat den toc do 450 Mbps (MCS 23).
  • May khach 1x1 su dung cac kenh 40 MHz co the dat den toc do 150 Mbps (MCS 7).
  • Tat ca may khach 11n deu bi han che o toc do 54 Mbps khi su dung bao mat WEP hoac WPA.
  • Toc do lon nhat co the se thay doi boi cac router va cac thiet lap may khach khac (chang han nhu viec tang do rong kenh, cho phep SGI). Mac du vay, neu cac tuy chon khong co du o ca hai dau, toc do lon nhat co the se phan anh kha nang toi thieu cua thiet bi (thuong la may khach).

 

- Dieu chinh toc do tu dong thuong la tot nhat, tuy nhien cac ket noi yeu doi khi co the duoc cai thien bang cach giam toc do lon nhat cua router. Nguoc lai, thong luong ket noi manh thuong duoc cai thien bang cach vo hieu hoa cac toc do cham hon. Tuy nhien can luu y mot dieu rang: Viec loai tru cac toc do thap co the huy ket noi cac may khach o xa hoac cu, trong khi do viec loai tru toc do cao lai doi hoi phai co khoang cach den cac khach gan hon hoac co cac may khach moi hon.

Hinh 10 a,b: Chon toc do va cac tuy chon du lieu cho router

11. Cuoi cung, neu may khach khong day cua ban ket noi va ping thanh cong nhung doi khi van xuat hien cac van de ket noi mang (chang han nhu mot so ping lam viec, mot so that bai), ban co the dang gap phai van de ve cuong do tin hieu, nhieu vo tuyen hoac su huy ket noi bi gay ra boi viec AP roaming. 

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Updated: 10/07/2010 | Views: 35 | Comments: 0

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